Using Semi-Analytical Method of FEM to computer three-dimensional infilling wave shape system, this article constructs a counterforce matrix. According to the Semi-Analytical Method of FEM, the placement field is expressed as a combination of the placements in two directions: one is a displacement showed by function; another is a system of algebraic equations used to solve FEM. In the end, the result shows that the Semi-Analytical Method of FEM has the advantages of high precision, quick convergence and easy to program.