For unequal diameter machining cylindrical cam profile based on double envelope principle, the practical profile equation and the profile machined by tool equation were given. The purpose of this study is explore new unequal diameter machining cylindrical cam method in the range of allowable error. According to the practical profile equation, the unequal diameter machining profile of cylindrical cam based on double envelope principle experiment were carried out. Considering the problem of accurate machining, three different diameter tool is used in the same cylindrical cam blank . And then, we used the software - Manufacturing Engineer XP to Program unequal diameter machining cylindrical cam Surface processing. The last, cylindrical cam surface was processed by CNC machining center.