A new compressed-air engine system based on three-stage single screw expander was proposed to improve the performance of power system.Three different structure styles were presented,and the studies on the power performance and the distribution of expansion ratios between stages were carried out by programming and mathematical modeling of each style.Research results indicated that the best matches of expansion ratios with equal heat temperature for the air tank of pressure 30 MPa were seven-five-three for“first-stage heating”style,eight-five-three for“two-stage heating”style and five-five-four for“three-stage heating”style,respectively.Results also showed that heating up inlet air or increasing the expander efficiency might improve the power performance.The output power of the“two-stage heating”style is far higher than that of“first-stage heating”style and is a little lower than that of“three-stage heating”style.The new system showed good structure and power performances. A new compressed-air engine system based on three-stage single screw expander was proposed to improve the performance of power system. Three different structure styles were presented, and the studies on the power performance and the distribution of expansion ratios between stages were carried out by programming and mathematical modeling of each style. Research results indicating that the best matches of expansion ratios with equal heat temperature for the air tank of pressure 30 MPa were seven-five-three for “first-stage heating” style, eight- five-three for “two-stage heating” style and five-five-four for “three-stage heating” style, respectively. Results. showed that heating up inlet air or increasing the expander efficiency might improve the power performance The output power of the “two-stage heating ” style is far higher than that of “first-stage heating ” style and is a little lower than that of “three-stage heating ” style.The new system showed good structure and power performances.