This article presents a modified FEM Superpostion method (S-FEM) for composite material analysis. Around the reinforcement body, failure and interface fracture may occur in the matrix. So the S-FEM was employed to detect the stress distribution around the reinforcement. One particle in big matrix is studied. Area of twice of particle radium is selected as local field.First, the feasibility of modified S-FEM is verified. And by symmetric analysis, geometric distribution of particle which may influence on the strength of composite material were discussed.