The resident ID card is a legal document issued by the state to prove a citizen's identity. According to the provisions of the "National Standard of the People's Republic of China GB11643-1999" regarding citizen identity numbers, the citizen identity number is a combination code consisting of 17 digits as the main code and 1 check digit. The order of the digits from left to right is: 6-digit address code, 8-digit birth date code, 3-digit sequence code, and 1 check digit.

The first 1-6 digits are the address code, indicating the administrative division code of the county (city, town, district) where the resident's permanent household registration is located in China.

The 7th to 14th digits are the birth date code, representing the year, month, and day of birth of the resident, according to the provisions of GB/T7408. The year, month, and day codes are not separated by any symbols.

The 15th to 17th digits are the sequence code, which is assigned to residents born on the same year, month, and day within the same address code area. The 15th and 16th digits are the allocation codes from the police station under the county or district-level government. Each police station allocation code has 10 consecutive numbers. The 17th digit represents gender, with odd numbers for males and even numbers for females. If there are two or more people born on the same year, month, and day, the next consecutive allocation codes (2nd, 3rd, 4th, 5th, etc.) are used.

The 18th digit is the check code, calculated based on the previous 17 digits according to the ISO 7064:1983.MOD 11-2 checksum calculation method.

With the ID card number, you can query information such as the issuing location, birth date, gender, and validity. The 15-digit ID card automatically converts to an 18-digit format. The first-generation ID card was a single-page card with a 15-digit code, which started to be used in 1984 and was discontinued on January 1, 2013. On January 1, 2004, the second-generation resident ID card with an 18-digit format began to be issued. The front of the card features the issuing authority, validity period, national emblem, certificate name, an artistic representation of the Great Wall, and colorful patterns. The back of the card includes seven registration items: name, gender, ethnicity, birth date, permanent address, citizen identity number, and a photo of the individual.