The purpose of this study is to investigate the performance of an autocascade refrigeration system by simulation and experiment using refrigerant mixtures of R744/134a and R744/290 as working fluid. Variations of mass flow rate of refrigerant, compressor work refrigeration capacity and COP with respect to mass fraction of R744/134a and R744/290 mixture were presented under different operating conditions. Performance test has been executed by ASRAE standard. Experimental results show as the composition of R744 in the refrigerant mixture increases, heating and coling capacity are enhanced, but COP trends to decrease. Experimental results are compared with those from the simulation.