Dual-rotor piston engine (DRPE) is a new type of differential rotary engine, with the pistons moving in a circle rather than linearly. Compared with the conventional engines, the complex valve systems can be omitted, and its power density is higher. In order to study the major performance indicators of DRPE, Matlab/simulink was used to simulate the zero-dimension model of its thermodynamic process. With regard to the characteristics of DRPE’s working process, the differential equations were established. Taking into account various period features, the equations were simplified. The ways to solve the major boundary conditions were found. Values of the mass, pressure and temperate were calculated according to different shaft angles. Then DRPE’s indicated mean effective pressure and power to weight ratio were calculated. Compared with some conventional internal combustion engines, the volume of DRPE’s chamber is used more efficiently, and its integral structure is more compact.