The tooth profile has significant effect on the engagement performance of harmonic drive (HD).In order to improve the engagement quality of HD, double-circular-arc and common tangent tooth profile (DCTP) as the tooth profile of flexspline (FS) were used, the conjugate existent domain (CED) and the conjugate tooth profile were established in Modified Kinematic Method, and the Least-squares fitting approach was adopted to fit it.The backlash, contact ratio, assembly state and relative movement trail were calculated to analyze the meshing performance of HD with a double-circular-arc and common tangent tooth profile.The results have shown that the tooth profile of the FS and the circular spline (CS) used with the DCTP remain continuous engagement, and the engagement point is changed continuously.Moreover, the double-engagement phenomenon is found, the theory conjugate arc length is 109.3mm, and the contact ratio reaches 69.03; compared with the harmonic drive with traditional involute tooth profile, the high engagement performance of harmonic drive can be obtained with the double-circular-arc and common tangent tooth profile.What's more, preferably selecting the coefficient of radial displacement is an important way to eliminate the interference of HD.