Abstract: Two dimension and three dimension finite element models of spur cylindrical gear with straight teeth are established using the modeling function of finite element software ANSYS.And the finite element analysis is conducted on the tooth root stress and deformation of the gear under static load.The comparison between the 2-D and 3-D model simulation results and that obtained by traditional calculation method of the gear strength is performed.At last, the shortage of traditional method for gear design is pointed out.The approach proposed in this paper provides a new design methodology and theoretical basis for gear design.