Abstract: In the stability analysis of deep excavation, the ground water pressure is divided into three parts,i. e.,hydrostatic pressure,seepage pressure and excessive pore water pressure. For the calculation of hydrostatic pressure,the errors of currently simplified methods used in practical engineering are pointed out,and a new method based on seepage analysis is proposed. The excessive pore water pressure induced by excavation should be determined by the undrained triaxial compression test according to the stress path of the soil in and out of foundation pit. Furthermore,the unloading shear strength parameters should be applied when using total stress method to analyse excavation problems.