Stiffened plate is a common structure form in plate and shell structure. There are important theoretical significance and project application value on studying dynamic response of stiffened plate subjected to air explosive loading. The motion equation of orthotropic plate which subjected to explosive loading is established adopting Lagrange’s equation of motion, and the stiffened plate where the stiffener is arranged uniformly is treated as textural orthotropic plate. Then the motion equation of the orthotropic plate is converted into motion equation of the stiffened plate. Therefore the maximum deformation of stiffened plate can be determined.