Abstract: In order to solve the problem of distribution and quantitative calculation of swelling load in the swelling soil foundation pit, this paper analyzes the distribution law of the humidity field in the swelling soil foundation pit from the theory of humidity stress field. It also calculates the magnitude of swelling stress using the coefficient of water absorption swelling stress measured by uniaxial continuous water absorption swelling test. The variation law of swelling stress with the depth of the foundation pit was derived using the humidity stress field theory. The variation law of water absorption swelling stress with the depth of the foundation pit was simulated using temperature stress. The law of variation of swelling stress with the depth of the pit is simplified and analyzed. The triangular distribution of swelling load with depth is derived for the foundation pit slope. Taking the weak swelling soil foundation pit in Chengdu as an example, we have used the classical Rankine earth pressure theory to calculate the earth pressure and the embedded depth of the cantilever pile in the foundation pit. The rationality and effectiveness of the theoretical calculation method for determining the excavation swelling load of swelling soil was verified by comparing the results of the F-SPW software with the displacement monitoring values obtained from the field excavation inclinometer.