Analytic solution and numerical solution are obtained for predicting tunnel water inflows and water head under the condition of an exponential decrease of hydraulic conductivity with depth in an isotropic jointed rock mass. According to the angle between the horizontal ground and non-flow boundary, analytical solution and finite-element solution are presented respectively. Effects of tunnel depth and non-flow boundary distance on predicted water inflow are discussed. A theoretic analysis is conducted to the enormous difference between the up and down water level in rock mass. The solution can be applied to forecasting the water inflows. A calculation example and its corresponding relation curves are given.