Abstract: The constraint conditions at pile head are assumed based on the case of Zhejiang Hotel Expansion Project, and then the deflection functions under different constraint conditions of pile tip and top are introduced. The total potential energy of pile-soil system is established based on the Winkler’s elastic beam theory. The expressions for the critical buckling capacity pile foundation under different constraint conditions are deduced by using the minimum potential energy principle. On this basis, the influence factors for the critical buckling capacity of pile foundation under different constraint conditions are analyzed. It is shown that the critical buckling capacity of pile foundation converges with the increase in the half-wave number. The convergence rate of the fixed pile head is the fastest, that of the hinge takes second place and that of the fixed with sway is the slowest. The constraint conditions at pile head affect the critical buckling capacity. The ratio of the critical buckling capacity of fixed pile head is the largest, that fixed with sway takes the second place and that of the hinge is the smallest at the same excavation depth. The ratio of critical buckling capacity of fixed pile head decreases slowly with the increasing excavation depth. However, the ratios the hinge and fixed with sway at pile head decrease rapidly.