Abstract: The Report to the 19th National Congress of the Communist Party of China clearly put forward the plan for universal participation in social insurance. It means both those low-income people who cannot afford or are reluctant to pay social insurance premiums and the vulnerable groups covered by social assistance will be included in the social insurance system. This inevitably leads to the expansion of social insurance function and its integration with social assistance. However，as important parts of the social security system，social insurance and social assistance differ fundamentally in their functions and this difference is currently not well understood in China. In the full implementation of the plan，it is necessary to handle the relevance and interaction of the functions of social insurance and social assistance. In the process，it is necessary to compare the advantage and disadvantage of the functions of social insurance and social assistance；based on it，the functions of social insurance and social assistance can be integrated，with the functional expansion of social insurance from mutual benefit to demand as the entry point and the functional promotion of social assistance from demand to mutual benefit as the acting point. This is conducive to the systematic optimization and overall stability of China’s universal social insurance

Key words: universal participation in social insurance, social insurance, social assistance, function integration