Chinese F Visa is issued to an alien who is invited to China for a visit, an investigation, a lecture, scientific-technological and culture exchanges.
After the new Foreigner Entry-Exit Administration Regulations took into effect on Sep. 1, 2013, there are 12 categories of ordinary China visas, instead of 8 categories.
F visas are less functional than before. If you want to do business, please apply for an M business visa. If you want to do short-term study, please apply for an X2 student visa.

Usually, the validity of a single entry, double entry or multiple entries (F) visa is 90 days or 180 days from the date of issue. This means the holder of the visa shall enter China no later than 90 days or 180 days from the date of issue, otherwise the visa will expire and is null and void. The duration of each stay of a (F) visa ranges from 30 to 120 days, which means the holder of the visa may stay in China for up to 30 to 120 days from the date of entry.

If you have entered into China with an F visa, and desire to stay in China longer than the valid period specified on your current visa, you can apply for an extension of the visa stay. The extension of the visa stay period by PSB is only effective for this entry into China. It does not affect the number of authorized entries or duration of each stay. Extension of the visa stay period will not exceed the stay period granted on visa.
It is a big improvement as before when you extended your visa, your current visa would be cancelled at the same time, whatever how many entries left.