According to the scroll expansion’s working principle, on the dynamic analysis of the scroll expander, the expression of the tangential force of the scroll tooth is obtained, and the expression of the output torque is obtained. The available work is pointed out, based on the universal principles of engineering thermodynamics, and expression of the effective thermal efficiency of scroll expansion is deduced combines with the aerodynamic power concept. Finally on the basis of theoretical research, the testbed is designed and the conclusion is proved through experiment which includes the relationship between the efficiency of the scroll expander and the inlet pressure, the volume flow rate and the rotational speed of the expander. It is pointed out that the influence of the internal leakage on the efficiency of the scroll expander. All this provides a theoretical basis for the improvement of the efficiency of the scroll expander.