This article presents the gear modeling method in dynamic mechanical analysis using SPH (Smoothed Particle Hydrodynamics) analysis method. The parameter equations of the transition curve of gear root and the other parts of gear are decided. The 3D discrete particles model is established based on the parameter equations. The SPH pre-process program of global and local dividing is developed. The error between the divided discrete particles and theoretical profiles of the gear has been analyzed. The analysis results show that this modeling method is a relatively better method and the correct SPH discrete particles can be divided by this method.