Abstract: The difference between water table and surface can bring abnormal pressure,which will cause effect on coalbed gas development.Considering the genetic mechanisms of abnormal pressure of reservoir,through simu-lation analysis on the mechanism of water table effecting reservoir pressure of different system,the variety of water table causing pressure variety of reservoir pressure is analyzed,which reflects the dynamic evolvement process of reservoir pressure under the action of hydrodynamic field.The study indicated that the variety of water table is an important mechanism of reservoir abnormal pressure.