A simplified life cycle cost (LCC) calculation model, which can be applied in project evaluation of open-loop surface water source heat pump system, was set up. Dest-c was used to do the annual energy consumption simulation for an engineering example, and the load demand was analyzed according to the model simulation results and combined with the performance curve of water source heat pump unit and variable frequency pump to calculate the LCC. The results show that water intake temperature, water drainage temperature and height difference between water intake and water drainage are the main factors which influence the LCC of open-loop surface water source heat pump system. By analyzing the above problems and through a further discussion on the measures of system optimization, a conclusion is drawn that, when the water intake temperature is 24 ℃，the best temperature difference between water intake and drainage is 7.7 ℃ under the operation condition of the constant temperature difference, while the minimum LCC is 441.80. In addition, taking into account the unit variant operation to improve the comprehensive energy efficiency of the system, a smaller LCC of 433.50 is obtained, demonstrating that the unit variant operation can further promote energy saving benefit.