To reduce energy use for space heating, the optimization of operation of heating system has always been a key issue in north China. In this study, on the basis of field survey results, one existing regulation mode of supply water temperature and its effects on indoor environment and energy use were analyzed. Then the simulation-based optimization method of supply water temperature was pointed out by comparing the relationship among outdoor temperature, indoor temperature, room base temperature and supply water temperature. The optimization effects were presented by comparing room indoor temperatures and energy consumption before and after optimization. As a result, the simulation-based method proposed in this study was proved to be an effective way to optimize the operation of heating system, by which “excessive heating” can be significantly decreased, and average daily indoor temperature can basically be kept at its set point.