To study the vertical load bearing capacity of large diameter steel composite pile with variable cross-section，a self-balanced pile test was carried out on 37# pile of Yushan bridge. The actual working condition is simulated by using the numerical simulation software ABAQUS. On the basis of verifying the correctness of the numerical model，the vertical load on the pile top was applied to the model，and the laws of axial force of the pile and the stress transfer of the steel pipe are analyzed. By changing the parameters of the variable cross-section positions，the models of different working conditions are established，and the influence of the variable cross-section positions on the vertical bearing capacity of the pile foundation is analyzed. The results show that：The Q-s curve of the self-balanced pile test had no abrupt change and was smooth. The bearing capacity of single pile is calculated to be 120056 kN，which is 3.14 times of the maximum design vertical load of single pile，and the pile foundation is safe enough；The results of the numerical simulation are in good agreement with the measured data，which proves that the numerical simulation method and the selection of parameters are satisfactory；The axial force of the pile above the variable cross-section position decreases slowly，and there is a sudden change in the axial force of the pile at the position of variable cross-section. The axial force of the pile below the variable cross-section decreases rapidly，and the pile end resistance exists at the bottom of the pile. The steel pipe is in the stage of elastic deformation and does not yield；The longer the pile section above the variable cross-section position，the stronger the pile resistance to vertical deformation，but in actual production，the amount of material usage should be considered to optimize the design.