The coordinate changing method used to bring the CAM theory profile of the eccentricity rotor tri-proportion controller was introduced in this paper.

The design of theoretical and actual CAM outline was set forth and their equations were given, which established the theoretical basis for the design and manufacture of the CAM with special outline.

After give out the coordinates of cam profile, the paper uses cubic spline interpolation to approximate the cam profile, which make theoryly result more practicable.