Abstract: A middle and deep ground source heat pump heating system with variable operating conditions and a thermal storage device is constructed. Based on the improved particle swarm optimization algorithm,the operation of the system is optimized with the operating cost,system coefficient of performance（COP）and geothermal energy utilization coefficient as objective functions,and the optimization results are compared and analyzed. The results show that the operating cost,system COP and geothermal energy utilization coefficient are 279.27 yuan,6.4420 and 0.8527,respectively. Taking the system COP as the objective function,the optimization effect is opposite to the operating cost,but similar to the geothermal energy utilization coefficient.