This paper establishes a model of R404a/CO₂ cascade refrigeration system with heat regenerator under the low-temperature environment. In order to improve coefficient of performance, a thermodynamic analysis are carried out. Through theoretical calculation,the influences of evaporation temperature, condensation temperature of low temperature cycle,the degree of supercooling as well as the temperature difference in the condenser evaporator on COP are contrasted and analyzed by control variable. The result showed that the degree of supercooling has obvious effect in improving COP when the other parameters are constant ;there exists a optimal value of condensation temperature of low temperature cycle makes COP to be maximum; COP increases with the increase of evaporation temperature and the temperature difference in the condenser evaporator while decreases with the increase of condensation temperature when the degree of supercooling is constant.