China's Marriage Law clearly stipulates that marriage is prohibited for direct relatives by blood and collateral relatives within three generations. It can be seen from this that indirect relatives and collateral relatives beyond three generations can marry. However, if they are direct relatives by blood or collateral relatives by blood within three generations, our marriage law prohibits them from marrying. Because close married couples carry too many of the same genes, the probability of children born to close married couples will increase dozens of times, or even hundreds of times. It is understood that children born to close married couples have the highest rate of albinism; The possibility of epilepsy is also high.
 Therefore, the law explicitly prohibits direct relatives by blood and collateral relatives within three generations from marrying. In real life, everyone generally knows that close relatives cannot marry, but some remote and difficult areas still have close relatives getting married. For the sake of marriage happiness and the health of future generations, we also hope that everyone will pay high attention to this and avoid marriage between direct relatives and collateral relatives within three generations.
 Legal basis:
 Article 7 of the Marriage Law of the People's Republic of China
 Marriage is prohibited under any of the following circumstances:
 （1） Direct blood relatives and collateral blood relatives within three generations;
 （2） Suffering from a disease that is medically considered unfit for marriage.
 Article 10 of the Marriage Law of the People's Republic of China
 Marriage is invalid under any of the following circumstances:
 （1） Bigamy;
 （2） Having relatives who are prohibited from marriage;
 （3） Having contracted a disease that is medically considered unfit for marriage before marriage and has not been cured after marriage;
 （4） Under the legal age of marriage.