The purpose of this research is aimed on inverse estimating the hydrogeological parameter of an inclined leaky aquifer. The processes of inverse problem is used to simulate the free surface of groundwater flow in not horizontal and saturated unconfined aquifer, namely the Boussinesq equation. An optimal procedure is proposed in this study to apply Conjugate Gradient Method to optimize the spatial distribution of the hydraulic conductivity and Adjoint State method is also used to enhance the efficiency of the optimization. A sand box test is also designed to verify the proposed inversed model In this way, the best spatial distribution of the hydrogeological parameters is expected to be identified under the limited computational effort, such as computing time and computing equipments. Furthermore, the groundwater flow can be simulated successfully.