In order to meet the requirements of freeform surface shape measurement, an optimization method of deformable mirror shape design for freeform surface partial compensation interferometry is proposed to overcome the problem that multi-parametric optimization is easy to fall into local optimization and can not effectively constrain the deformation range of deformable mirror. The optical simulation system is established based on the principle of ray tracing, and the deformable mirror shape is characterized by Zernike polynomials. The deformation range of deformable mirror is constrained by calculating the vector height of the surface, and an optimal solution model with constraint conditions is constructed with the wavefront as the optimization objective. Based on the nodal aberration theory, the optimization variables are selected, and the global optimal solution is found by combining the simulated annealing algorithm. In order to measure a typical freeform surface, a catadioptric partial compensator based on deformable mirror is designed. The simulation results show that the method can reduce the peak valley value of residual wavefront from 32.20λ to 6.55λ, and the maximum residual wavefront slope from 0.53(λ·pixel-1) to 0.11(λ·pixel-1), which meets the requirements of partial compensation detection.