Abstract: In this paper, the perturbation based on displacement method was extended to the field of circuit, which is used to solve the nonlinear LC circuit equation, and an analytical method for the research of nonlinear LC circuits was provided. Deducing from the Lagrange function of the system, the variational equation was discretized by the finite element to obtain the time stiffness matrix. The characteristic equation of the circuit was perturbed for the first time, and the original time stiffness matrix was replaced by a perturbed approximate stiffness matrix. On the basis of the relationship between the stiffness matrix and the transfer matrix, the problem was transformed into the problem of symplectic transfer matrix, and the oscillation characteristics of the LC circuit can be solved. The comparison between the perturbation based on displacement method and the fourth order Runge Kutta method demonstrated the correctness of the proposed method. Compared with the transfer symplectic matrix method, it is proved that the proposed method has definite precision, efficiency and stability.