Why do Chinese people need a visa to travel abroad?

Requiring an extra visa or exit permit from citizens is not very common today but historically, that's why passports were invented (and not to restrict immigration) and the reason for that is simple: a large population was seen as the bedrock of power. You need many young people (and especially men) for labor-intensive industries and for the army. In many countries, passports are still used to prevent people from leaving but to a much more limited extent (for example by forcing people investigated for a serious crime to surrender their passport).

In richer countries, seeing large number of people leave is slightly less of an issue now (although in some parts of East Germany, Poland, and recently Spain, Portugal, Greece, the number of young, educated people leaving is actually a concern) and restricting citizens' rights to address it is not considered acceptable. Consequently, citizens enjoy a very strong right to come and go as they please within the country, to leave it and to reenter it without conditions (you will at most find some form of financial incentives, like grants that require to stay or come back to your country/region of origin or extra benefits for families).

There are many countries in the world where civil liberties don't weight so heavily in the balance and freedom of movement both within and out or in the country are simply not guaranteed. This type of restrictions is most famously associated with Warsaw Pact or Soviet Bloc countries but freedom of movement is not so tightly linked with capitalism as it might seem at first glance.

To be sure, the most liberal and democratic countries (e.g. in Western Europe) all have market economies but some also had severe restrictions on the movement of their population until the mid-19th century. On the other hand, China has been able to introduce increasing amounts of private ownership and trade in its economy without fully opening its society. Similarly, Russia's internal passports predate the Soviet Union, which just continued and extended a system that existed in Imperial Russia.

Here is a really interesting site that attempts to explain all the problems that Chinese citizens suffer in order to travel abroad: http://www.why-so-hard-chinese-travel-abroad.com/

Much of it seems to be down to difficulty and cost of acquiring a passport and visas. Passport acquisition: Requires multiple visits to home province irrespective of where the person currently lives. Visa costs: Many countries make it expensive to acquire a visa for Chinese citizens. Visa documentation: Many countries require extensive documentation and justification for Chinese travellers

This site also provides information on Chinese exit controls and restrict exit in the following cases:

Article 12. Under any of the following circumstances, Chinese citizens are not allowed to exit China:

Hold no valid exit/entry documents, or refuse or evade border inspection;

Are sentenced to criminal punishments, the execution of which have not been completed, or are suspects or defendants in criminal cases;

Are involved in unsettled civil cases and not allowed to exit China upon decision of the people's courts;

Are subject to criminal punishment for impairing border administration, or are repatriated by other countries or regions due to illegal exit from China, illegal residence or illegal employment, and the No-Exit-from-China period has not expired;

May endanger national security or interests, and are not allowed to exit China upon decision by competent departments under the State Council;

Hopefully this wont provoke any politically charged responses, but I believe it (at least to some minor extent) has to do with keeping Chinese people in China.

It's very well known that the living conditions in some parts of China, and in some professions (think factory workers) are very bad compared to most of the western world. If you look at metropolitan areas in Canada and the U.S. (primarily, however this also applies to other countries) you'll see a very large population of naturalised 2nd, 3rd etc generation Chinese people. Due to the population of China, even a small percentage of emigrants translates to large numbers of people leaving the country.

China is a country where a lot of its strength comes from it's large population, and therefore large workforce (being a high export-manufacture nation). So for me it seems only natural that the government would want as little of its people to be leaving the country without a good reason, especially if they have no visa and seek only to seek asylum elsewhere.

The more blocks they place on traveling abroad, the less people will leave the country permanently in my opinion.

Of course this is just my take on it, and I may be completely and utterly wrong.

There is definitely no exit visa required for Chinese citizens. The immigration control checks if a traveler has the visa for the destination solely.

If a Chinese citizen go to the visa-free countires, like Thailand, Indonesia, Jeju-island of S. Korea, Morocco, Maldives..., a passport is enough.

The existing answers treat China as if the situation there is very fundamentally different from other countries (like the US). However, residents from both countries have areas that they need a visa for, and areas that don't need a visa/permit at all.

Sure, the no-visa country list is shorter for China than the US, but the chinese list will likely keep growing and the point is that it is there.

That still leaves the question why people need visas at all, but as that is already covered, I will just mention that it seems that migration control, and 'tourist tax' appear to be the main reasons for visas nowadays.