The invention discloses a clamping device on a screen frame flanger. The initial end of a solid shaft and conical locking blocks are fixed through a nut; dovetail guide way sliding blocks are fixed to the conical locking blocks correspondingly; each dovetail guide way sliding block is correspondingly connected with an arc-shaped clamping plate through rib plates to form a sliding block assembly; all the arc-shaped clamping plates are in end-to-end connection with one another through locking springs and hanging hooks; dovetail guide ways on the dovetail guide way sliding blocks are matched with dovetail grooves in a locking tray for assembling; the locking tray and a hollow shaft are welded; the other end of the solid shaft penetrates through the hollow shaft and the bottom of the other end of the solid shaft is connected with a rotary mechanism; the rotary mechanism and a hydraulic cylinder are fixed through a nut; the hydraulic cylinder is fixed to the bottom of a rack; a belt wheel is disposed at the bottom of the hollow shaft and driven to rotate through a triangle belt by a motor; and a support shell is welded to a working table top, and the working table top is supported through a support. According to the technical scheme, the clamping device belongs to a clamping mechanism on the flanger, a workpiece can be firmly clamped during flanging of the workpiece, the effect that the workpiece does not tilt is guaranteed, and assembling is convenient.