Stray light is a key issue that must be considered in the TianQin telescope. To solve the problem of a long simulation time and the inability of the simulation results to be fed back to guide the optical design, we propose a fast estimation method for stray light based on the FOV with high accuracy. Compared to other models, the error between our model and the software simulation results is smaller, within one order of magnitude. Based on this method, we obtain the optical component target of the TianQin telescope and propose an optimization method to reduce stray light, which can be verified by analyzing the optimized optical design.