The temperature of water used for surface water source heat pump（WSHP） could make dynamic changes in the condition of heat or cold rejection. When the water temperature is over the amount of heat or cold rejection that water can take, WSHP system will run irregularly even paralyze. Based on twodimensional model of the initial water temperature, dynamic model of water used for WSHP was proposed with mass equation and energy equation. And with flow equation coupled with temperature equation, the equation of water temperature changes in load was obtained.