The damage mechanism of inner-stiffened cylindrical shell subjected to pulsation and collapse-jet loads from underwater explosion bubbles was analyzed, and the influences of some physical quantities, such as structural parameters, location of satchel charges etc., on the structural deformation characteristics and damage mode were investigated. The research results show that the global structural deformation are mainly caused by the UNDEX bubble expansion impact, and the high speed bubble collapse jet (velocity>100m/s) can cause serious local damage of the structure. Analyses also indicate that the elastic-plastic boundary effect and the free surface effect have significant influence on the shape of the UNDEX bubble.