Harmonic drive has widespread applications for its compact size and high reduction ratios. It is often favored for electro-mechanical systems with space and weight limitation. In order to minimize the volume and improve its transmission capacity, more and more aborative design technologies are adopted. For structural analyses in assembly state and in transmission stage, Finite Element Analysis (FEA) can be widely applied to get proper parameters and performance. Flexspline usually endures large deformation under assembly force from wave generator. In transmission state, driving force leads to multiple tooth mesh contact between flexspline and circular spline teeth. In this paper, shell element is applied to build flexspline cone, and tapered beam element is used to model the teeth on the flexspline. Contact relation between flexspline and wave generator is simulated by contact element. Forced displacement of flexspline is imposed by contact analysis. Transmission forces are acted at the teeth tips on the flexspline in mesh state, whose values are determined according to experimental distribution. Simulations of assembly state and transmission state are computed in ANSYS. Deformation and stress distribution in assembly state are compared with that in transmission state. Some suggestions for long life and high performance design are present.