Abstract: Several abnormal changes of water temperature in Shahe observation well have been recorded since the observation. In order to explore the causes, FFT and S transformation methods are used to analyze the observed data. It is found that there is a good correspondence between the abnormal data changes and the microearthquakes within the range of 5km and the medium-strong earthquakes within the range of 200 km of the nearby faults in the next three months, indicating that the water temperature observation of the well has a good pre-earthquake abnormal response characteristics. The results show that the low frequency wave and diurnal tide are the main causes of the abnormal water temperature data. In addition, the diurnal tide has a significant influence on the data in the process of accelerated change before multiple earthquakes and after rapid change, and even appears the diurnal tide shape, which can be taken as one of the indicators to determine the abnormal water temperature data of the well.