Selection of initial structural parameters is an essential step for the zoom system design. In this paper, a new method based on Gaussian optics and Particle Swarm Optimization (PSO) algorithm is proposed to design initial structural parameters of the zoom system, and an optical automatic optimization design is carried out based on the initial structural parameters. Firstly, displacement parameters of the zoom group and the compensation group of the zoom system are derived based on Gaussian optics. Secondly, constraints of the zoom system are established using the PSO algorithm, and a fitness function is designed. Then, the initial structure parameters of the zoom system are optimized. Finally, uniform and monotonic movement of the cam curve is achieved in an example of a 6 × zoom system. The results indicate that our proposed methods improve the efficiency and accuracy of the zoom system design, which has guiding significance for the design of multi-group moving zoom system with high zoom ratio and other engineering applications.