Abstract: In order to study the distribution of earth pressure for limited soil between oblique support retaining foundation pit and adjacent basement, back analysis of site monitoring data of a foundation pit was studied. Based on the improved cubic spline method of the trial algorithm, Matlab software was used to calculate the bending moment value of the supporting structure and the earth pressure value behind the pile. The results show the earth pressure of limited soil is influenced by displacement mode, non-limit state and boundary conditions. The active earth pressure of limited soil above the excavation surface shows a distinct "R" shape distribution. The active earth pressure is about 16.3% smaller than that of the calculated value of classical earth pressure. The difference between the passive earth pressure and the active earth pressure below the excavation surface shows approximately rectangular distribution. The difference is about 65% smaller than that of the calculated value of classical earth pressure. The above analysis results provide the basis and reference for the design calculation of this type of engineering.