The invention belongs to the field of design of internal combustion engines and relates to a cam rotor internal combustion engine power system design method, in particular to a cam rotor internal combustion engine design method. In the design method, according to cam lift and size changes, caused by the cam lift, of the contour surface of a cam; other surfaces of the cam are wrapped through the inner surface of an inner cavity rotation surface component, the outer surface of an outer rotation surface component and corresponding end components in a contact sealing mode, and then an unsymmetrical annular gap is formed; the cam is made to do fixed-axis rotation along with one of the inner cavity component and the outer rotation surface component relative to the other one; a set of cam driven parts are mounted on the inner cavity component or the outer rotation surface which is not fixed to the cam. According to the design method, the four classic procedures of the otto cycle are realized through volume change, and the influence on the rotational speed is little. A control system is used in cooperation to realize flexible transformation of various working modes. The adaptability is high. The system is good in designability and especially suitable for being used in cooperation with computers to conduct flexible automatic control.