Based on the model of the endoreversible heat pump, the irreversible steady flow model of heatpump has been founded with a constant parameter expressing the heat leak, and a coefficient expressing irreversibility except heat resistance and heat leak, such as friction, turbulence, nonequalisum, and so on. The relation between the optimal coefficient of performance of heat pump and the heating load has been derived according to the law of heat transfer q ∝ΔTn. The results obtained herein involve many results in recent literature. Based on the model of the endoreversible heat pump, the irreversible steady flow model of heatpump has been established with a constant parameter expressing the heat leak, and a coefficient expressing irreversible except heat resistance and heat leak, such as friction, turbulence, nonequalisum, and so on. The relation between the optimal coefficient of performance of heat pump and the heating load has been derived according to the law of heat transfer q αΔTn. The results obtain herein involve many results in recent literature.