The method of discontinuous deformation analysis (DDA) is used to simulate the chaotic pendulum. Firstly, a two-degree-of-freedom model and a four-degree-of-freedom chaotic pendulum model with undamped nonlinear free vibration are established. The motion differential equations of the two models are derived and the theoretical solutions of the pendulum angles under two degrees of freedom are obtained by Matlab. The original DDA equation is simplified, the rigid DDA equation is derived, and the DDA program is written by Matlab. The motion of two kinds of pendulum is simulated numerically. The time history diagrams of different pendulum bars under the two models are obtained respectively, and the applicability of the program is illustrated by comparing with the theoretical results.