Objective To investigate the effects of social participation, intergenerational rearing and their interaction on cognitive function of the elderly in China. Methods The relevant data of 5 563 elderly people ≥ 60 years old were collected from the 2018 Chinese health and retirement longitudinal study (CHARLS). Logistic regression was used to analyze the influencing factors of cognitive function of the elderly. Social participation and intergenerational rearing were taken as two interactive items to evaluate the influence of social participation and intergenerational rearing interaction on the cognitive function of the elderly, adjusting confounding factors. Results There were 2 338 (42.03%) elderly people with cognitive impairment. There were significant differences in the incidence of cognitive impairment among the elderly with different ages (χ²=74.614, P<0.05), gender (χ²=94.481, P<0.05), education (χ²=44.116, P<0.05), marital status (χ²=93.358, P<0.05), ethnic group (χ²=8.015, P<0.05), and self-rated health (χ²=39.348, P<0.05). After controlling the related variables, the results of multivariate logistic regression showed that social participation (OR=1.580, 95%CI: 1.411-1.768), low intensity intergenerational support (OR=1.271, 95%CI: 0.962-1.680), and high intensity intergenerational support (OR=1.197, 95%CI: 1.056-1.358) within one month were protective factors for normal cognitive function of the elderly. The results of interaction showed that there were multiplicative and additive interaction (OR=1.855, 95%CI: 1.563-2.202) between social participation and intergenerational rearing on the normal cognitive ability of the elderly. The values of RERI (95%CI), API (95%CI), and Index S (95%CI) were 0.388 (0.230-0.545), 0.201 (0.119-0.283), and 1.719 (1.284-2.301), respectively. Conclusion Social participation and intergenerational rearing are the protective factors of cognitive function of the elderly, and there is an interaction between them. [ABSTRACT FROM AUTHOR]