According to the analysis of heat balance, about 1/3 of the fuel combustion heat is taken away into the ambience by exhaust gas of diesel engine. Depending on the characteristics of the diesel, this paper uses a special system to recover this waste heat, in which the organic Rankine cycle is combined with a single screw expander. The economy should be improved by using this system in the diesel. The model of this system is designed in Matlab combined with REFPROP. Using this way, the thermodynamic parameters should be calculated and the thermodynamic properties of this system with different working fluids should be analyzed. At last, R245fa, R245ca, R123 and R141b are selected as the alternative refrigerants used in this system.