In order to analyze the contact stress and deformation distribution during the assembly of flexspine in a hollow-type harmonic reducer, finite element simulations were carried out using ANSYS software. Results indicated that the stress concentrations were found at the connection between gear ring and the barrel as well as at the feet of the gear teeth. When the rigid wheel was assembled, the flexspine gear ring was bended due to the constraint by rigid wheel, which enlarged the stress on the flexspine by around 11%. Deformation and strain measurement on the flexspine during assembly was implemented using 3D optical measurement system. Measurement results match with the numerical simulation which validates the accuracy of the simulation method. As a result, the maximum VonMises stress during the assembly at the flexspine is 622 MPa, which has a great impact on its reliability. This research offers a data support for design and operation of the harmonic reducer.