Abstract: On the basis of the partial differential equations of water level in a deep well that is affected by the bulk strain tide and the boundary conditions of mutual permeation between the aquifer and the well the solutions of the equations have been obtained by the superposition principle, impulse theorem and separation of the variations. Some suitable values are given to the parameters of well aquifer in the solutions. By means of numerical calculation the relations among the well tide coefficients and phase lags and parameters of the well aquifer are discussed. The phase lag phenomenon of response of the well water level to earth tides is better interpreted. The studies of the parameters and the graphs obtained show that the larger the radius of the well casing, the porosity of the aquifer and the bulk compressibility of solid matrix of the aquifer, and the smaller the permeability of the aquifer, the smaller is the tidal coefficient of well water level; while the greater is the phase lag for well water level to respond to the earth tide. The reaponse of the well water level to the tide of longer periods is better than that to the shorter-period tides.