Abstract: In order to realize the requirements of large aperture and long focal length zoom optical system in photoelectric tracking equipment and by analyzing and calculating the zoom principle, the suitable initial structure was determined, then the mechanical compensation zoom type was adopted to realize the whole zoom system through analysis and comparison. The entire system needs to be designed to achieve a continuous zoom of 100 mm ~ 600 mm, while ensuring that its F number does not change, and because of the large aperture and long range of focal length change, the design is more difficult.The final result obtained through optimizing design show that the total length of the whole system is 563.956 mm, and the F number remains almost unchanged, which can be used to realize remote imaging in practical applications. When the focal length of the system is medium and short, its modulation transfer function (MTF) value is more than 0.4 at the 30 lp/mm, and its performance decreases slightly in the long focal length, which meets the requirements for practical applications.