Through the temperature measurement of the geothermal reinjection well in the Dezhou Shuiwen residential area, the paper dicussed the variation characteristics of geothermal field in five sections in depth, and especially analyzed the heat recovery source of sandstone reservoir. The results show that during largescale productive reinjection, low temperature return water will significantly reduce the sandstone reservoir temperature around the reinjection well, and the recovery rate is particularly slow. Qualitative analysis and quantitative calculation show that the role of the geothermal heat flow and the top formation heat conduction is extremely weak in the heat recovery source of the reservoir, while the main source is the peripheral highertemperature formation in the same layer and heat carried by the flow of the geothermal water. Based on the results of this study, under the conditions of largescale reinjection, thermal breakthrough is inevitable. Therefore, it is very necessary to carry out research on reasonable distance between production and reinjection wells, in order to prevent thermal breakthrough in a short time.