Assisting substance users to recover from the behaviour of drug addiction and maintain long-term rehabilitation is a long and complicated process, in which the motivation to undergo drug rehabilitation plays a decisive role. So far, the cultural connotation of family and its mechanism of promoting behavioural change of substance users have not been fully explored. Through in-depth interviews with 15 drug rehabilitants, among which there were 7 women and 8 men, it is found that the motivation for drug rehabilitation is stimulated under the guidance and restriction of family ethics based on obligation and responsibility, which is mainly reflected in the longitudinal intergenerational responsibility. On the one hand, negative consequences such as intergenerational liability deficit and reputation damage lead substance users to reflect on ethical values. On the other hand, disciplines such as intergenerational responsibility and obligation and mutual assistance can correct the actual behaviour of substance users in ethical practice. In contrast to Western countries, which focus on external environmental factors such as family function, family relationships and family support, the motivation for drug rehabilitation in China places more emphasis on their identity and role as family members and corresponding responsibilities, which provides inspiration for developing social work services for substance users from family cultural norms.