The average reservoir pressure and water influx rate are two important parameters for reservoir with active bottom water. The paper, based on the model of KEITH, provides a solution by inversion of Laplace and Hankel, and obtains the relation between the average dimensionless reservoir pressure and water influx. If one is known, then the other can to be confirmed correctly. Compared with solution method of material balance, the affection of anisotropy is considered. In addition, sensitivity analysis of affecting factors on reservoir pressure is presented.