Abstract: Taking the project of Lanzhou rail transit Line 1 crossing the Yu′ergou Bridge as the research background, MIDAS\|Civil software is used for numerical simulation of the project, the axial force variation law and the vertical displacement of existing pile and underpinning pile before and after underpinning are analyzed. Through the indoor model test, the bearing capacity of pile foundation is discussed. The results show that the maximum vertical displacement of pile foundation occurs at the pedestal top of two piles which are truncated at the same time, the load sharing ratio of underpinning piles with the distance of the existing piles from near to far is 29.3% and 19.8%, and the load sharing ratio of the existing piles is 40.6%. The maximum tensile stress value is 1.69 MPa, appearing at the position where a pile is truncated, and the load sharing ratio of numerical simulation cap is 10.3%, the variation range of load sharing ratio is 14.1%～14.85% in the indoor model test.