The first step in building construction is to excavate the foundation pit，there are many factors affecting the stability of the foundation pit and surrounding buildings，the study of foundation pits often ignores the effects of precipitation seepage and the non-saturation effects. Inversion of monitoring parameters based on Beidou GNSS,considering the effect of non-saturation,based on a foundation pit excavation project in Changde, Hunan Province, the whole process of construction was simulated. And, the internal support axial force, seepage and non-saturation effects, and the stress distribution outside the pit are analyzed and studied. The results show that①The disturbance of the soil outside the pit during the foundation pit excavation stage is relatively larger than that of the supporting construction stage;②The effect of unsaturated effect on the stability of foundation pit is small and is mainly reflected in the influence of soil settlement on the pit outside it;③Tensile stress concentration occurs at the inner support of the four corners of the rectangular foundation pit.