Under barometric pressure,groundwater flow in well-aquifer systems is a kind of hydro-mechanical coupling problem.Applying the flux boundary conditions on borehole wall and water pressure equilibrium conditions inside and outside the borehole wall under barometric pressure(BP),an analytic solution to well-water level changes has been proposed in this paper.The formulation shows that the BP coefficients increase with time and tend to BP constant.The Change of BP coefficients over time depends only on the ratio of transmissivity(T) to the well radius squared(r2w),and has nothing to do with the change in BP.The BP constant only relates to aquifer loading efficiency(B),and has nothing to do with the aquifer transmissivity and well radius.The BP coefficients change over time in the analytic formulation is consistent with the analysis of measured data from the Nanxi wells.Based on the BP coefficient changes over time,a parameter estimation method is suggested and discussed in its application to the estimation of the aquifer BP constant(or B) and transmissivity by using the Nanxi well data. Under barometric pressure, groundwater flow in well-aquifer systems is a kind of hydro-mechanical coupling problem. Applying the flux boundary conditions on borehole wall and water pressure equilibrium conditions inside and outside the borehole wall under barometric pressure (BP), an analytic solution to well-water level changes has been proposed in this paper. The formulation shows that the BP coefficients increase with time and tend to BP constant. The Change of BP coefficients over time depends only on the ratio of transmissivity (T) to the well radius squared (r2w), and has nothing to do with the change in BP. BP only only to aquifer loading efficiency (B), and has nothing to do with the aquifer transmissivity and well radius. The BP coefficients  change over time in the analytic formulation is consistent with the analysis of measured data from the Nanxi wells.Based on the BP coefficient changes over time, a parameter estimation method is suggested and discussed in its application ion to the estimation of the aquifer BP constant (or B) and transmissivity by using the Nanxi well data.