Abstract: In Yongnian-Beidu well, there are two kinds of water thermometer to monitor the well water temperature. One is the ZKGD3000-NT type and the other is SZW-1 type digital thermometer. Water temperature at the depth of 250 m and well water temperature gradient recorded by these two kinds of water thermometers are compared and analyzed. Results show that water temperature gradient recorded by these two instruments has the same law: well water temperature and depth were positively correlated with no anomaly. For dynamic observation, the SZW-1 type is more stable and the well temperature at the depth of 250 m is about 22.58℃ with stable upward trend and small changing rate. While the well water temperature observed by the ZKGD3000-NT installed at the same depth is much unstable with downward trend and large changing rate.