According to research, the earliest crime was sexual crime, followed by crime concepts such as theft and murder. As early as the mixed marriage period in primitive society, although the relationship between the sexes was "completely free", there were restrictions on the time and place of sexual intercourse. For example, "There is actually a Jizi who is sexually fond of promiscuity and spends the day in the market. The emperor was angry and let him go to the southwest." "("Lu Shi. Preface" Volume 5 "Youchao Family"). This shows that primitive society already punished those who had sex in public during the day with exile. After entering class society, sexual laws gradually developed. However, due to changes in dynasties, changes in monarchs, innovations in concepts, changes in customs, etc., the understanding and handling of sexual behavior and legal and illegal sexual relations are often different. The main features are as follows:

1. Encourage early marriage and early childbearing. In ancient times, the population was sparse. In order to speed up population reproduction, early marriage and early childbearing were encouraged. From Emperor Wu of the Later Zhou Dynasty to Kaiwujian of the Tang Dynasty, the minimum age for marriage was 15 years old for men and 13 years old for women. Those who do not marry after reaching the marriageable age will be punished. Emperor Hui of the Han Dynasty once issued an order: "If a woman is not married between fifteen and thirty years old, she will pay five times the head tax."

2. The regulations restricting marriage are stricter and the penalties for violators are heavier. The main restrictions include: people with the same surname are not allowed to marry, close relatives are not allowed to marry, people with serious illnesses are not allowed to marry, adulterers and adulterers are not allowed to marry, etc. "Tang Law" records: "Those who marry with the same surname will each stay for three years." "Ming Lv" records: "Anyone who marries a person of the same sex will be punished with a rod of sixty and divorce." Anyone who marries a relative will be punished differently according to their closeness, ranging from a cane and a prison sentence to beheading and hanging.

3. Husband’s sexual privilege and wife’s sexual repression, as well as polygamy of the ruling class and monogamy of the ruled class. During the period of the Five Emperors, the emperor's wives were divided into principal and deputy. Both Huangdi and Emperor Ku had one principal wife and three secondary wives. Shun had three wives. During the third generation, the names and numbers of emperors' wives increased. In the Zhou Dynasty, there were 121 wives, and there were countless concubines. The princes also had one main wife, second wife, six female concubines and eight concubines. Each of the ministers had one wife and two concubines. A scholar had one wife and one concubine, while those below the rank of common people had one husband and one wife. Men above the rank of scholar can have multiple wives, but women should stay together.

Illegal sexual behavior, types of sexual relations and punishments: In the late Spring and Autumn Period, sons, nephews and younger brothers were allowed to marry the wives and concubines of uncles and brothers (except biological mothers), and elders were also allowed to have sex with the wives and concubines of younger generations. But some people think this move is inappropriate. Both "Qin Code" and "Han Code" prohibit an adopted son from raping his adopted mother. considers an adopted son to rape his adoptive mother as a serious crime against ethics and should be shot to death. Both the Ming Code and the Qing Code stipulate that rape should be punished by hanging and an eighty-year-old cane; raping a girl under the age of twelve is the same as rape. The Law of the Tang Dynasty stipulates that if an ordinary person commits adultery, the prison term will be one and a half years; if a slave commits adultery with his beloved, the prison term will be two and a half years; if he commits adultery with a relative, the prison term will be three years until hanging; if a rapist commits rape, the prison term will be two years, but if a slave rapes his beloved, the prison term will be two and a half years. Anyone who commits adultery against his father, grandfather, concubine, uncle, aunt, sister, descendant's wife, or brother's daughter shall be hanged. The Song and Tang Dynasties are the same.

In addition, in order to maintain ethical standards, certain sexual crimes are punished severely. "Historical Records of Criminal Law of the Yuan Dynasty" records: "If a husband seizes his wife and the wife resists arrest, he is not guilty of murder." The Ming and Qing Dynasties Code contains: "The husband or the adulterer who has been caught by adultery shall not be killed immediately." "Tang Code" The "Laws of Household Marriage" contains: "Anyone who has a wife and takes another wife will be punished for one year." In the Zhou Dynasty, there was a stipulation that "men and women who do not have a righteous relationship will be sentenced to death in the palace."