The objectives of this study are to predict actual system performance and effective operating range of the 2-stage compression heat pump system using river water. An electronic expansion valve was applied to the simulation to analyze the effects of operating conditions on the system performance. The developed program was verified by comparing the predictions with the measured data. The results from the present model showed a good agreement with the measured data. In addition, the heat pump simulation was conducted by increasing condenser reservoir inlet temperature to investigate the benefits of the 2-stage compression over the 1-stage compression in the heating mode. The performance of the 2-stage compression cycle was better than that of the 1-stage compression when the inlet temperature of the condenser reservoir was higher than $40^{circ}C$.