The 3 D model of worm and helical gear is established based on UG by the equation of tooth surface and the data point. On the basis of Hyper Mesh,the pretreatment of the finite element model including mesh generation,applying constrains,setting contact condition,etc. is carried out. By using FEM,the analysis of dynamic contact from the double teeth-meshing to the single teeth-meshing and then to the double teeth-meshing is carried out to simulate the changes of the tooth contact stress and shape under the actual working conditions and to find the characteristics of engagement about plastic worm and steel helical gear,steel worm and steel helical gear. The samples including steel helical gear,plastic worm and steel worm are machined by hobbing,injection and turning respectively,then used to wear test on the basic of the micro-transmission test platform,the results show that the contact stress and fluctuation in the meshing process of plastic worm is small,and it has the better wear resistance.