In mechanical compensation zoom optical system, the zoom can be achieved through the zoom curve to control the movement of the zoom group and the compensation group. Therefore, it is very necessary to fit a good zoom curve to make the imaging of zoom optical system clear and stable during the zoom process. In this paper, the dynamic optical theory, CODE V and ZEMAX macro are used individually to fit zoom curve for a 20× zoom optical system, then the corresponding movement curve equations can be generated. According to the three groups of curve equations, several random zoom position points are selected and evaluated in defocus and MTF of central field and edge field. Through the analysis of the data, the zoom curve fitted by the dynamic optical theory can meet the system requirements, and it is better to ensure the image plane stable.