In China, social security number generally refers to social security number, i.e. citizen ID number, and its generation rules are determined according to the national standard GB 11643-1999 "Citizen ID Number". Citizen ID number is a characteristic combination code, consisting of 17-digit body code and 1-digit check code. The arrangement order from left to right is: 6-digit address code, 8-digit date of birth code, 3-digit sequence code and 1-digit check code. - **Address code**: Indicates the administrative division code of the county (city, banner, district) where the coded object's permanent residence is located, and is implemented in accordance with the provisions of GB/T 2260. For example, the address code of Dongcheng District, Beijing may be 110101. - **Date of birth code**: Indicates the year, month and day of birth of the coded object, and is implemented in accordance with the provisions of GB/T 7408. No separator is used between the year, month and day codes. For example, born on January 1, 1980, the code is 19800101. - **Sequence code**: It indicates the sequence number assigned to people born in the same year, month and day within the area identified by the same address code. Odd numbers of the sequence code are assigned to males, and even numbers are assigned to females. For example, the first male born in the same area on the same day of the same month of the same year may have a sequence code of 001; the first female may have a sequence code of 002. - **Check code**: It is a check code calculated according to the ISO 7064:1983.MOD 11-2 check code based on the previous 17 digits. For example, the ID card number is 11010119800101001X, where 110101 is the address code of Dongcheng District, Beijing, 19800101 is the date of birth code, 001 is the sequence code, 1 represents male, and X is the check code. Through such rules, everyone has a unique social security number, which is used to accurately identify personal identity information in various social affairs such as the social security system.