Based on ANSYS, this paper conducts a simulation study on the external pressure buckling of a cylindrical shell with initial defects. First, the eigenvalue buckling analysis of the ideal cylindrical shell is carried out, and the first thirty order linear buckling modes are obtained as the initial geometric defects. Secondly, the single modal defect method and the combined modal defect method are used to establish the model with initial geometric defects. The nonlinear buckling analysis is performed by the non-linear stabilization algorithm and the arc-length method of the finite element method. Then, the critical buckling load is obtained by the static pressure buckling experiment of the cylindrical pressure shell. Finally, the results of nonlinear buckling analysis are compared with the experimental results and the calculation results of pressure-bearing structure engineering design methods. The results show that the arc-length method has higher prediction accuracy than the non-linear stability algorithm. The results obtained by the engineering design method of pressure-bearing structures are conservative, and the critical buckling load is much lower than the experimental results. The first-order modal defect is not the initial defect that has the greatest impact on the critical buckling load, the order of the most unfavorable initial defect is generally low. The amplitude of the initial defect in the model has a great influence on the critical buckling pressure, but it has little influence on the modal order of the most unfavorable initial defect. The above two initial defect construction methods are effective, but the low-order multi-modal combined defect model has higher prediction accuracy with an error of about 3.55%.