Abstract: In order to study the resistance intensity to external pressure of casing,finite element model was adopted with 20 space nodal,and combined with substructure method,analyzed the resistance intensity of casing string theoretically.Used interactive mode with restrict and release boundary,calculated stress along axis of casing string by finite element model based on integrate attribution of substructure.Used high accuracy triangle cell,analyzed resistance intensity effect rule of worn geometry default to casing string.Calculated displacement field distribution rule of casing string at external pressure by SOR method.Study indicate that substructure method can be used to exactly calculate the resistance to external pressure along axis of casing string,the intensity of resistance to external pressure decreased with deep increase of polishing scratch.