Abstract: In the light of the inherent drawbacks in the existing adjusting compound element conductivity matrix to calculate unconfined seepage,an improved method of adjusting compound element conductivity matrix is proposed.The free surface elements are divided into the dry elements and the wet elements and the transitional elements,and the penalty function method with double parameters is applied to the transitional elements intersected by free surface.Based on the groundwater flow quantity equivalent effect,the permeability coefficient of the actual seepage field is adjusted so as to precisely consider partial saturation and unsaturation.The unstability integration number near the Gauss point is overcome,and the calculating precision and the convergence speed are improved.Meanwhile,a new method for computing the boundary integration is proposed in free surface seepage field.The method was proven to be effective and feasible by examples and projects.