The contrate harmonic gear drive has different characteristics from the radial harmonic gear drive

such as the axial deformation in contrate harmonic drive produces the contrate flexspline deformation and thus produces the relative movement by meshing with the contrate circular spline. The depth of engaging and the mashing backlash are the quality index for analyzing and evaluating its meshing performance. The nominal pressure angle

deformation regulation and the deformative value of contrate flexspline are the main factors effecting on the depth of engaging and meshing backlash. This paper analyzes the effects of the nominal pressure angle and the maximum deformation upon the depth of eng aging and meshing backlash using an established method of meshing analysis and calculation and drawings made by computer and then obtains some useful conclusions. It provides the basis for choicing the suitable meshing and structural parameters for contrate harmonic gear drive.