Abstract: According to the characteristics of large FOV high zoom ratio wideband optical system, a 38 zoom ratio was designed, the primary and advanced aberrations of large FOV wideband system were balanced by using the mechanical compensation technique of changing root, the h-hp diagram and the aperture diagram analysis. A method using the cam formula to calculate the displacement of compensation group with no parfocality by programming and modify the design value of cam curve in Code V was put forward. This method ensured the parfocality of the high zoom ratio optical system.