A large number of problems in natural sciences (physics, chemistry, biology, astronomy, etc.) and the social sciences (engineering, economic, military, etc.) can be described by using differential equations. In this paper, we study two kinds of differential equations, i.e., the first order differential equation and the second order differential equation, and give the definitions of equilibrium point and stable equilibrium point. Moreover, we discuss the judgment methods of stable equilibrium point, and give the application of stable equilibrium point in the species coexistence problem.