A method for determining a reduction factor of a bearing capacity of an axial load cylindrical shell structure is described. In the method, a depression defect is introduced in a manner of applying a radial disturbance load. Then, an influence rule of a depression defect amplitude of a single point to an axial load bearing capacity is analyzed by using numerical values; then, defect sensitivity analysis is performed on depression defects of multiple points; then, experiment design sampling is performed by using load amplitude values and load position distribution as design variables; and finally, the most disadvantageous disturbance load of the multiple points that limits the defect amplitude is searched for, and a reduction factor of the bearing capacity of the axial load cylindrical shell structure is determined.