For the purpose of improving the engagement qualities of harmonic drive（ HD）,taking the HD with the drive ratio 100 as example,the basic conjugated tooth profile for involute tooth profile is calculated based on the modified kinematics method of HD and the elastic deformation of flexspline,the tooth profile optimization design model is established and calculated by using the iteration method of MATLAB,in order to verify the correctness of the aforementioned model,the engagement state of the tooth profile after optimized is studied.The results show that effective conjugate exist domain and effective conjugate tooth profile are found,in order to avoid the interference during the engagement process,the three-dimensional tooth profile must be applied as the conjugate tooth profile.Finally,the correctness of all of the aforementioned model are verified by the characteristics,such as non-interference during the assembly and movement process,more number of teeth participated in engagement and large transmission ratio.