Social insurance has the nature of basic guarantee, national compulsion, mutual assistance and social welfare. Basic guarantee refers to ensuring people's basic living, so that they can still get basic living guarantee after losing their labor remuneration. State compulsion means that the society must pay the fees according to the prescribed rate, and can't decide whether to participate on its own like commercial insurance. Mutual assistance is organized according to the principle that society bears risks. Social insurance costs are generally shared by the state, units and individuals, and social insurance funds are established. Social insurance fund agencies pay insurance benefits and provide services through unified adjustment and mutual aid, and implement income and redistribution, so that workers (or citizens) who have participated in social insurance in society can be effectively guaranteed in their basic lives. Social welfare means that social insurance benefits generally benefit every worker who is eligible for social insurance benefits, and social insurance undertakings are generally managed by non-profit public authorities. Social insurance fund agencies should ensure the appreciation of the fund and solve the maximum social insurance problem.