Negative-pressure flange positioning device

The invention belongs to the field of workpiece clamping devices and particularly relates to a negative-pressure flange positioning device, comprising a rack; the rack is provided with a positioning terrace; the center of the positioning terrace is provided with a positioning spigot; the bottom, at the positioning spigot, of the positioning terrace is provided with a drain port in penetrating manner. The negative-pressure flange positioning device also comprises a compressing mechanism and a water suction pipe. The compressing mechanism comprises a first piston cylinder, a transmission gear, asecond piston cylinder and a wedged plate; the transmission gear is rotationally connected to the rack; both the first piston cylinder and the second piston cylinder are fixed to the positioning terrace; both the first piston rod and the second piston rod are provided with gear teeth; the transmission gear is engaged between the first piston rod and the second piston rod; the other end of the second piston rod is abutted