Abstract: The design of the cam curves of the zoom system is critical to keep the precise, smooth and balance movement of the optical system. The article analyzes the characteristics of equal space design (ESD) and equal angle step design (EASD), the former means the motion of zoom group is linear to turning angle of cam and the cam curves are expanded as a beeline, the latter means the focus is linear to turning angle of cam. A solution to overcome the shortcomings of these design methods is proposed, which combines the merits on their adaptable zoom segments. At last, a kind of cam assistant design software OZSAD (optical zoom system assistant design software) V1.2 is introduced, which can conveniently and quickly meet all three kinds of design requirements. It is proved that the pressure angle of cam curve, the total expanded angle and the points of cam curve could be effectively reduced. Therefore, the design precision could be reached.