In order to investigate the meshing force of the tooth surface of the plastic helical gear and the steel worm in the transmission process,the mechanical model of the meshing pair of plastic helical gear and steel worm is established by considering the load distribution between the meshing teeth. By using the deformation compatibility in the gear meshing process,the variation of the contact point meshing force of the tooth surface of the plastic helical gear in the continuous meshing process is calculated. And the meshing force of the plastic helical gear and the steel worm is analyzed with the ANSYS Workbench finite element software. The calculation examples show that the results obtained by the method are in good agreement with the simulation results of the finite element method,which proves that the proposed method is reasonable and effective. The research shows that the maximum meshing force of plastic helical gears in the normal meshing process appears in the small tooth meshing area near the tooth root,so the plastic helical gears are prone to wear and fatigue damage.The fast calculation of meshing force between plastic helical gear and steel worm is realized by the proposed method,some references for gear design and gear loading capacity improved in engineering can be provided.