Zoom cam is a pivotal part used for driving every lens group in zoom lens, the design result of cam curve is decisive importance for motion property and system precision as well as system imaging in zoom system, therefore, zoom cam design is an important part of the zoom lens design, a fine cam performance is the basic requirements to reach lens design of image quality goal and optical zoom process. a new method is presented in this article, it adopts the method of piecewise processing to establish several common functions in steep interval so as to make the arc length non-uniform and to segment the arc length equally in the smooth curve. The initial cam curve of an optical system is optimized and analyzed, the results show that when the arc length is divided by the power function, the cam curve can be significantly improved, the pressure angle of the curve can be reduced, and the optimized curve is smooth and without inflection point, which can effectively improve the overall performance of the cam. © 2018 SPIE.