The observation of water temperature in deep wells has been carried out for more than 20 years in China.However,study on the mechanism of water temperature response to earthquakes is inadequate.During the study of the co-seismic response characteristics of water level and temperature in 121 wells within the China subsurface fluid monitoring network at the time of the December 26,2004,M-S8.7 Indonesia earthquake,we found regular response characteristics,that is,when the water level in a deep well oscillates,the water temperature in the same well will mostly experience a cycle from dropping to restoration at the same time.The process will continue for dozens of minutes to several hours.In order to confirm the observed phenomenon,we collected the digital water level and temperature observation data for 39 far-field strong earthquakes from the Tangshan well in Hebei Province(with the data set beginning in 2001).The same response characteristics were observed.Based on the analysis of the influencing factors that may cause the water temperature drop,the authors suggest the gas escape mechanism for co-seismic water temperature drop and posit two main factors that influence the water temperature drop during the process of gas escape.Finally,the authors provide a rational explanation of some observed phenomena based on the mechanism. The observation of water temperature in deep wells has been carried out for more than 20 years in China. However, study on the mechanism of water temperature response to earthquakes is inadequate. Fluid of the study of the co-seismic response characteristics of water level and temperature in 121 wells within the China subsurface fluid monitoring network at the time of the December 26, 2004, M-S8.7 Indonesia earthquake, we found regular response characteristics, that is, when the water level in a deep well oscillates, the water temperature in the same well will mostly experience a cycle from dropping to restoration at the same time. the process will continue for dozens of minutes to several hours. order confirm confirm the observed phenomenon, we collected the digital water level and temperature observation data for 39 far-field strong earthquakes from the Tangshan well in Hebei Province (with the data set beginning in 2001). The same response characteristics were observed. Based on the analysis of the in fluencing factors that may cause the water temperature drop, the authors suggest the gas escape mechanism for co-seismic water temperature drop and posit two main factors that influence the water temperature drop during the process of gas escape. Finally, the authors provide a rational explanation of some observed phenomena based on the mechanism.