Abstract: The groundwater temperature, which is related to the selection of heat exchanger and the whole system optimization design, is an important parameter for design of groundwater source heat pump system. Periodical monitoring of groundwater temperature in each layer in the geothermal well prospecting and utilization and predicting the changes in groundwater temperature with depth are very important in providing reference information for design and operation of groundwater source heat pump system and for well completion technology and other processes. Based on the groundwater temperature data measured in depths from 30 to 108m of two observation wells in Xi’an Jinghe development zone, a GM(1,1) model for a non-equidistant sequence is established to forecast the change trend of groundwater temperature in depths from 128 to 150m based on grey theory. The result shows that the model can forecast the change trend of groundwater temperature with depth. It is a new method for the study of the vertical change in groundwater temperature.