In this paper, by the relaxation technique, the relaxation modulus-based matrix splitting iteration method is presented for solving a class of nonlinear complementarity problems. The convergence conditions are given when the system matrix is a positive definite matrix or an H-matrix. The strategy of the choice of the relaxation parameters is discussed. Numerical examples show that the proposed method is efficient and accelerates the convergence performance of the modulus-based matrix splitting iteration method and the projection-based matrix splitting iteration method.