Abstract: A cam rotary engine power system of internal combustion type, making use of the cam and a plurality of cam followers to form cam mechanisms, and forming a plurality of circumferential distributed sealing working chambers with the inner-cavity-member, the external-rotating-surface-member and the end-cover-member. The volume of those chambers change with the relative rotation of the cam and the cam followers, in which the intake, compression, power and exhaust processes of the Otto cycle are completed by valve coordination. The chemical energy produced by gas combustion is directly converted into the mechanical energy of the rotor in the form of fixed axis rotation. The power system does not set the crankshaft of piston engine, and the high pressure gas directly drives the rotor to rotate and output power. The structure of this power system is relatively simple and its parameters can be adjusted in a wide range.