Abstract: Mencius opposes the view that human nature is regarded as a material and benevolence and righteousness as a finished product made after birth. Mencius believes that such a view will lead to the "disaster of benevolence and righteousness". In the history of thought, this is actually the expression of human nature represented by "Zhuangzi ·Pianmu", that is, emphasizing the truth of human nature and opposing the good made after birth with the truth. Mencius' theory of human nature regards benevolence and righteousness as the content of human nature, and also takes truth in good. In fact, Mencius' theory of human nature is the unity of truth and good, and the ultimate realization of human nature is the natural development of human nature.