Abstract: The optical design softwares ZEMAX and Python were used to realize the precision solution of optical path difference (OPD) for spatial gravitational wave telescope.The dynamic data exchange(DDE) closed-loop communication between ZEMAX and Python was realized. First, the Python software processed the data of telescope mirror after the finite element analysis, and transmitted the analysis results to the ZEMAX with DDE for tracing ray.Secondly, the ZEMAX software transferred the ray coordinate value to the Python software through the DDE. Lastly, the Python software calculated the OPD and wavefront changes caused by rigid body translation through the global coordinate system. Through simulating the deformation of the gravitational wave telescope with the temperature change of 1 mK, the OPD and wavefront variation of the spatial gravitational wave telescope was solved by means of ZEMAX software and Python software. The results show that the OPD precision reaches the order of 1e-13 meter, which can satisfy the requirements of telescope for pico-level stability.It is concluded that the method is feasible to calculate the OPD, and it provides a technical reference for the OPD analysis for the further mechanism design of the gravitational wave telescope.