Abstract: A method of three-dimensional finite element mesh generation for the multiphase composite with r andomly distributed grain is presented, and an automatic modeling tool is given for the research of microstructure using FEM. The criteria of conflictoverlap of any two ellipsoidal aggregates are proposed based on a volume-index, and a numerical method of three-dimensional r andom aggregate model is realized. The polarization of mesh is resolved in the finite element surface mesh generation based on traditional mapping approach coupled with local connection approach. The three-dimensional AFT method is improved to generate tetrahedron mesh of matrix and grains. By utilizing the characteristics of AFT, all the grains are meshed to tetrahedrons atone time. The proposed method lays down the foundation for further multi-scale computation between microstructure and macro-mechanical performances of the multiphase composite. Some examples are given to demonstrate the validity of the method.