In this paper, the formulas estimating aquifer parameters have been reduced. From well tide observations of well No. 6 in Gansu province, the author calculated rocky porosity n, well-aquifer equivalent volume, rocky, elasticity modulus Ea and sensitivity η for using the well-aquifer as strain instrument. Changes of these parameters might reflect the changes of subsurface rock structure and strain case. It is significant to study these changes for predicting earthquake.