The current world situation of an increasing population is leading to an increase in the fuel consumption, green house gas emissions, electrical power consumption etc. These increases are becoming a serious problem which various organizations are concerned about and are trying to solve. An increase of bus air conditioning systems increases fuel consumption and therefore produces green house gas emissions as conventional bus air conditioners are vapor compression systems driven by engine power. In order to reduce the fuel consumption and gas emission of a bus, a two stage ejector cooling system is selected to study because the system requires little electrical power or engine power to drive the system. It uses exhaust gas emissions from buses to drive. The two stage ejector cooling system is used to cool condensate from the condenser of a bus air conditioner to a subcooling state in order to enhance the performance of vapor compression system.The objective of this research is to study in theoretical and experimental performances of a two stage ejector cooling system using the waste heat of the engine (exhaust gases). To develop a combined air conditioning system with a two stage ejector cooling subsystem and a vapor compression subsystem and evaluating the applications of a two stage ejector cooling system to enhance the performance of the traditional bus air conditioning (vapor compression system). The cooling capacity obtained from the two stage ejector cooling subsystem is in turn used to cool the condensate of the vapor compression subsystem to a subcooled state to increase the COP of the vapor compression subsystem. The ejector cooling system uses water as the working fluid; the design operating conditions have a generating temperature of150℃, a condensing temperature of54℃and an evaporating temperature of13℃, In this work, variables were tested in order to understand the application of the system and the effect of varying operating conditions. In addition, the comparison of the performance between the single stage and two stage ejector cooling system has been carried out.The results indicate that a two stage ejector cooling system can decrease the temperature of the condensate from the condenser from54℃to26.5℃under operating conditions with a generating temperature of150℃and an evaporating temperature of21.7℃, of which the COPejc is0.37. If condensate from the condenser of a vapor compression system is cooled by the two stage ejector cooling system under these conditions, the liquid becomes a subcooled state at26.5℃, the COPVCS improves from3.6to4.85(+34.86%). Furthermore, in this study, under high evaporating temperature condition, the two stage ejector system had lower performance than that of the single stage ejector system. The two stage ejector system showed better performance than the single stage ejector when used at a low evaporating temperature.The expected advantages of the proposed system are reduced fuel consumption, reduced green house gas emissions, less demand for power from the engine, much less vibration while working and very low noise output, except that of circulating pump.