Abstract: In order to find out the utmost external pressure sustained by the ring-stiffened cylindrical shell which is damaged with a large local indentation but not destroyed, the concept of residual strength is proposed. By using a dimple shaped indentation to describe the typical shape of damage, the stress distribution and buckling pressure of a damaged ring-stiffened cylindrical shell subjected to hydrostatic pressure are calculated with MSC/NASTRAN. Compared these results with an ideal ring-stiffened cylindrical shell, the duration capacity of pressure hull varying with the position and range of the indentation is analyzed. In order to assess the residual strength of the ring-stiffened cylindrical shell, a residual strength coefficient is proposed and a series of curves of the coefficient are drawn.