Harmonic　drives　are　the　core　components　to　enable　movement　in　industrial　robots.　Unfortunately,　the　deformation　of　flexspline　causes　obvious　partial　axial　load　on　gear　engagement.　This　synthetic　error　leads　to　a　series　of　additional　problems,　such　as　the　deterioration　of　transmission　quality,　and　the　reduction　of　both　precision　and　fatigue　life.　This　study　focuses　on　a　harmonic　drive　with　a　double　circular-arc　tooth　profile.　A　coordinate　transformation　is　carried　out　based　on　the　kinematics　of　harmonic　drives.　On　this　basis,　the　conjugate　tooth　profile　of　a　circular　spline　is　derived.　A　simulation　model　is　developed　based　on　the　motion　relationship　for　harmonic　transmission.　The　effect　of　inhomogeneity　of　the　load　distribution　on　the　surface　of　the　gear　teeth　was　investigated　using　the　partial　axial-load　index.　The　effect　of　different　factors　on　the　partial　axial　load　is　analyzed.　To　reduce　the　effect　of　partial　axial　load　of　flexspline,　we　select　a　suitable　material　and　wall　thickness.　For　a　certain　practical　range,　both　tooth　width　and　chamfering　of　the　flexspline　teeth　help　reduce　the　partial　axial　load　and　increase　the　flexspline　length.　These　conclusions　enable　improvements　of　future　designs　of　reliable　flexspline.