To study the stress of plastic helical gears in the new type car door lock under the working condition,establish the finite element model of helical gear mesh through ABAQUS,the contact process of plastic helical gears is simulated and analyzed based on nonlinear contact algorithm,and obtain the contact stress and bending stress of plastic helical gears. According to Lewis equation and gear Hertz stress theory to calculate the stress of the plastic helical gear meshing process,and compare with the finite element simulation results. The results verify the strength of plastic gears meet actual requirements,and point out the maximum contact stress in the normal engagement process appears in the double teeth meshing zone,the maximum bending stress appears in the three teeth meshing zone,gear prone to fatigue failure in those positions,propose advice to improve the strength of the gear teeth. The study prodives theory basis for the strength analysis of plastic gears.