In order to study the variation characteristics of the main control factors of groundwater temperature under the long-term influence of ground source heat pump, Anyang 5th People's hospital was chosen as the study area and the temperature field of groundwater was treated as a grey system. The study uses grey relational calculation method to analyze relation among groundwater temperature, groundwater depth, temperature, precipitation and water temperature of recharge wells, and to gain the main control factor of groundwater temperature. Results show that groundwater depth is the main control factor without the influence of groundwater source heat pump, while temperature, precipitation, groundwater depth and water temperature of recharge well would corporately affect the groundwater temperature under the influence of groundwater source heat pump: the influence of water temperature of recharge wells on the water temperature of the monitoring wells decreases with the increase of the depth vertically, and the main control factor of the groundwater temperature would change from water temperature of recharge well to groundwater depth, while the influence of the water temperature of recharge wells on the water temperature of the monitoring wells decreases with the increase of the distance horizontally, and the main control factor would change from water temperature of recharge well to temperature and groundwater depth.