Abstract: The recording earthquake ability Mst of the water level of a deep well can flect the state of underground stress field, which is the magnitude difference between Mt and Ms,where Ms is determined by a regional seismostation network, Mt is the magnitude of a coming earthquake from the level data of a deep well. 1 559 water level data related to earthquake of three deep wells is used to calculate the earthquake magnitudes and then these Mt are compared with the earthquake magnitudes Ms. These results show that these Mt are with the confidence level of 97.5%, the Rvalue is 0.5 and the Wallenvalue is 0.54. 623 maximum values of each month is used and these Mt are with confidence level of 97.5%, the Rvalue is 0.42 and the Wallenvalue is 0.42. In the 16 years period past, the practice shows that the water level observation data analysis is a helpful method for earthquake prediction.