Abstract: Lagrange Discontinous Deformation Analysis (LDDA) can be used to solve contact nonlinear problem. Compared with other methods, LDDA has many advantages. First, its joint simulation is truer and more natural then DDA; secondly, its contact force can achieve highly accurate solution due to equilibrium iteration. In this paper, LDDA’s primary formulae are derived, a new iterative algorithm for dynamic contact forces is introduced, in which the relax factor is chosen by physical property other than by mathematic theory. The application example indicates that the algorithm has high calculating efficiency. Thusly, an effective measure and implement for contact analysis will be provided.