The effects of an ejector in a refrigeration cycle with carbon dioxide oil its cooling capacity and cooling coefficient of performance were numerically analyzed. The effects of an ejector oil the entrainment ratio of vapor mixing ill suction flow, pressure difference of the Suction chamber, environmental temperature, lower side pressure and higher side pressure were numerically investigated. The cooling coefficient of performance and cooling capacity decrease with an increace in vapor quality in Suction flown Furthermore, the cooling coefficient of performance and cooling capacity increase with an increase in pressure difference of the suction chamber. When the environmental temperature is low, the evaporator inlet pressure is low and the compressor discharge pressure is high., all ejector gives a larger cooling coefficient of performance and cooling capacity.