A calculation model for designing and analysing the tooth bending stress of plastic gears is presented in this paper. Material properties were assigned with hyperelastic properties using plastic material. On the basis of plastic gear design calculation standards, the process of calculating the design, analysing according to bending strength, and studying the influence of geometric parameters on bending strength such as: modulus m, pressure angle α, root fillet radius ρ. Simulate bending strength on FEA software and use response surfaces method to determine the influence of factors on bending strength and thereby select the optimal set of geometric parameters according to the bending strength.