Abstract: Underwater explosion-induced cavitation loading damages ship structures significantly. To clarify cavitation formation mechanism during near-field explosions at ship bottom and plate bending stiffness’s influence on cavitation, underwater explosion experiments were conducted. 2.5g TNT equivalent explosives were detonated at different distances from fixed square plates. Experimental results show that velocity difference between the plate and surrounding water during bubble contraction causes cavitation. Both the maximum cavitation volume and closure pressure decrease with increased bending stiffness. To explore bending stiffness’s influence mechanism on cavitation, numerical simulations were performed via ABAQUS software with CEL method. Simulations used aluminum and polyurethane material parameters under consistent bending stiffness. For plates with same bending stiffness, their cavitation region sizes are basically identical regardless of materials. The maximum cavitation volume decays exponentially with the bending stiffness increase. Fitting formulas for cavitation volume under different bending stiffness are provided.