First of all, it is divided into first order, second order, linear and nonlinear. According to the textbook: generally, the elementary integration method of the first-order equation is discussed first, and then one kind, which can be divided into homogeneous, linear, Bernoulli, appropriate and integral factors, can be simplified. Then it is explained that the elementary integral method should not be used more, and then the theory: the existence and uniqueness theorem. . . Then focus on linearity. Homogeneous constant coefficient characteristic root method, inhomogeneous constant coefficient undetermined coefficient method, liouville theorem. . . . .