Validity
Validity of a visa refers to the period that the visa holder is allowed to enter China. Unless otherwise specified, a visa holder may enter China at any time prior to expiry of validity (right up to midnight Beijing Time on the final day of validity), so long as the entries granted on the visa have not been used up. 

A visa becomes effective from the date of issuance. The visa automatically becomes invalid once its period of validity expires regardless of whether its entries are used up or not.

Chinese embassies and consulates general do not extend the validity of an issued visa. A fresh application is needed after the expiry of the issued visa. Foreigners holding an expired visa seeking entry will be refused. Make sure the visa is valid before you set off for China. However, even if a foreigner holds a valid visa, he or she might be refused entry by the immigration authorities.

Example:

Q: I hold a double entry visa valid until June 20 and the first entry occurs on June 12. Can I come to China again for the second entry on June 25?

A: No, you will be refused to enter China as the visa had expired before the attempt to use the second entry. 

Number of Entries of a Visa
The number of entries of a visa refers to the number of times the visa holder is permitted to enter China within the visa’s validity. When the entries are all used up, the visa is no longer valid. Even if there are still unused entries, the visa is not valid either if its validity has already expired. In either case, the visa holder should apply for a new visa if another visit to China is planned. An applicant will be refused entry to China if all the visa entries have been used up.

Example:

Q: I hold a double-entry visa valid from March 20 to June 20, and have entered China twice before May 20. Can I continue to use this visa again before June 20?

A: No,you have used all the entries permitted by the visa.

Duration of Stay
Duration of stay of a visa refers to the longest period the visa holder is allowed to stay in China from the day following entry to China on each visit.

Example 1:

Q: I hold a single-entry visa with duration of stay of 30 days, and enter China on June 12. When is the last day I can stay in China lawfully permitted by the visa?

A: The last day is July 12 as the duration of stay is counted from June 13, the day after entry.

Example 2:

Q: I hold a single-entry visa for a stay up to 30 days and validity until June 12. If I enter China on June 12, the last day of validity, can I stay in China for 30 days thereafter? 

A: Yes.

After entry into China, a foreign citizen who needs to stay in China longer than the duration of stay permitted by the visa must apply for an extension of stay at a local public security bureau before the original permitted period of stay expires. This does not necessarily mean your application for an extension will be approved. The applicant shall bear any consequences arising from this situation.

Overstay in China violates the country’s laws and regulations on control of the entry and exit of foreigners, and could result in a fine or other penalty.