Abstract: The design of heliostat field in the tower solar thermal power generation system is studied, and the corresponding efficiency calculation and parameter optimization model are established according to the plane optical law and the layout strategy.Firstly, Monte Carlo method is applied to establish the computational model of shadow occlusion efficiency and truncation efficiency, thus obtaining the computational model of optical mirror field efficiency. After comparing different optimization strategies of mirror field layout, the occlusion free layout is selected as the optimization strategy, and the optimization model of mirror field parameters that can meet the output power requirements is provided. The variable step size search algorithm is used to solve the mirror field parameters values. Finally, the optical efficiency and output power under different heliostat field designs are calculated and compared with those before optimization. Finally, the calculated annual average optical efficiency of the optimized heliostat field is 63%, the annual average shadow occlusion efficiency is 94.9%, the annual average cutoff efficiency is 78.17%, and the average annual average output thermal power of the mirror per unit area can reach 0.7312 kW/m². Compared with the performance of the heliostat field before parameter optimization, the performance is significantly improved, such as the average annual output thermal power of 60.2933MW after optimization is increased by 91.57% compared with that before optimization.