Abstract: The micro steel pipe piles in the basis replacement of buildings in loess high fill area generally has a large slenderness ratio, thusly it is prone to buckling failure. In order to analyze its buckling stability under axial load, a method for calculating the critical buckling load of micro-tubular pile in soil under axial load is proposed upon the static equilibrium method. The method uses Pasternak two-parameter foundation beam method to calculate the pile side soil horizontal resistance and takes into account the influence of pile side negative friction. Then, the correctness of the method is verified by comparing with experimental results and numerical simulation results. On this basis, it is analyzed that the influence of soil horizontal resistance, of the resistance of negative friction, of the stiffness of pile and Length of pile exposed to ground on the buckling critical load. The research shows that the shear interaction between soil mass at the pile side has a great influence on the buckling critical load. However, the negative friction force slightly reduces the buckling critical load. Under the constraints of the soil at the pile side, the buckling destruction of the pile is determined by the upper half of the pile. Increasing the pile stiffness near the pile top can effectively improve the buckling critical load.