The reliability and safety of MEMS parts are important factors in industrial MEMS applications, Most MEMS parts are made from multigrain polysilicon, an orthotropic material with random material direction. Analyzing the stress and displacement and knowing the effective material constant are important when using MEMS in industrial applications. We developed a computer program to calculate the effective material constant of poly silicon using the boundary element method with the microstructure evolution method. The results obtained using the boundary element method were compared to those obtained using the finite element method to confirm the validity of the program.