Matrix filling and equation solving are the most computationally-expensive steps in the method of moments (MoM). Based on the compressed sensing (CS) theory, an improved method of MoM is proposed in this paper. Through introducing sparse transform matrix, the unknown response can be expressed sparsely, so we can construct and optimally solving underdetermined equation under the framework of CS. Numerical examples show that the proposed method can reduce the matrix filling cost dramatically, and also can improve the efficiency of equation solving effectively.