The invention relates to the field of rotation mechanisms, in particular to a pneumatic opening mechanism of a rotary check platform. The pneumatic opening mechanism of the rotary check platform can conveniently and fast carry out all-dimensional check on a large and heavy workpiece and comprises a base. A supporting bearing is arranged on the base. A rotatable rotation frame is arranged on the supporting bearing and comprises a front rotation frame and a rear rotation frame. The lower end of the middle of the front rotation frame and the lower end of the middle of the rear rotation frame are provided with floating frames which are connected with the rotation frame through springs. The lower ends of the floating frames are connected with tensioning devices which can be disengaged from the floating frames. The tensioning devices can achieve up-and-down movement of the floating frames through the springs. Horizontal rods are fixedly installed at the upper end of the middle of the front rotation frame and the upper end of the middle of the rear rotation frame. Upper clamping blocks corresponding to the floating frames are arranged on the horizontal rods.