Visa Policy of China

China uses - and always sticks to - a tit for tat principle. That is, China sets visa policies depending on its counterparts in other countries. For example, if your country has strict visa policies against China, then it's very likely that China will do the same. If your country's visa is costly for Chinese citizens, you may also need to spend a considerable amount of money for a China visa. Visa-exemption policies for certain countries are also on the basis of bilateral agreements.
 

China requires visitors to get a visa in advance unless they are eligible under the visa-free policies, which are mostly applicable to tourists transferring in China or citizens of countries who have signed bilateral visa waiver agreements with China. Holders of a valid Chinese Temporary Residence Permit or Permanent Residence Permit can also enter China without a visa.
 

China can issue a visa on arrival at Shenzhen, Zhuhai, Xiamen, and Hainan, but not for all countries. The rules change every now and then, thus VOA is not recommended. To guarantee you a smooth trip, get your China visa in advance. In addition to the cities mentioned above, other port cities also issue VOA but only in urgent situations.
 

1. Prepare your documents: passport, visa application form, travel itinerary, invitation letter, etc.
2. Make an appointment for China visa application submission with Chinese embassy / consulate / Visa Service Application Center (CVASC). 
2. Submit your application to the Chinese embassy / consulate / CVASC at the appointed time.
3. Collect your passport and visa on the appointed date and pay the fee. One may need to pay the fee when submitting the application in some countries. 

See more details:
Visa Application Requirements
China Visa Mail Service
China Visa Fees

It is common sense that consular officers won't tell you the reasons for approving or rejecting a visa application. However, certain factors may cause your application to be rejected, such as your nationality, previous experiences and records, and your country's relation with China.

The rules are not normally applied to their fullest extent but at any time the government may apply the regulations more strictly against an individual, to applicants from certain nations, or when special events are taking place such as the Olympic Games. Thus, at any time you might be asked to supply full travel bookings, show a minimum amount of funds, or have invitations from Chinese individuals or organizations.
 

Hong Kong and Macau have different immigration systems from mainland China. In comparison, their visa policies are much looser than that of mainland China. Many countries enjoy visa-free entry to Hong Kong and Macau, with a granted stay duration raging from 7 days to 180 days, depending on the visitor's nationality. Because of the differences in border control policies, a Chinese visa cannot be used to enter Hong Kong or Macau. A separate visa should be obtained if your country is not on the visa-free list.

 Further Reading:
Do I Need A Visa for Guangzhou If Traveling from Hong Kong?
How to Apply a China Visa in Hong Kong