Taken the cylindrical shell pile leg of the offshore platform as the research object, the buckling characteristics of stainless steel cylindrical shell under local corrosion and non-corrosion conditions are studied, and the local regional uniform thinning of the cylindrical shell is used to simulate the corrosion of pile leg. The initial defect measurement, axial compression test and numerical calculation are carried out for a group of unthinned intact cylindrical shells and a group of thinned corroded cylindrical shells. The critical buckling load of the cylindrical shell is obtained through experiments. The first 50 order modal defects and buckling eigenvalues of the shell are obtained by linear buckling analysis of the shell. The Riks arc length method is used to perform nonlinear buckling analysis of the first 50 order modal defects with initial defect amplitude, and the equilibrium curve and critical load of the shell are obtained. On this basis, the influence of initial defects on the buckling of stainless steel shell subjected to local corrosion and not subjected to local corrosion is studied, and their worst modes are investigated under the condition of multi-mode defects. The results show that: the corroded shell is less sensitive to initial defects and different modal defects than the uncorroded shell; for stainless steel cylindrical shells, the worst modal defects are not of order 1 as commonly thought, but may also occur in higher order modes.