Mechanism for positioning welding fixture

The invention discloses a mechanism for positioning a welding fixture. The mechanism comprises limiting devices, the welding fixture and a locking device, wherein the limiting devices comprise bases I, supporting frames and first rollers; the welding fixture comprises a base II, wheels, guiding tables and positioning-clamping units; the locking device comprises a fixing frame, an air cylinder and a rotating arm. When the mechanism is in use, the to-be-used welding fixture is moved to a position between the two limiting devices, and then the lower end surfaces of the two guiding tables are matched with the roller surfaces of the first rollers; when the welding fixture is pushed, the guiding tables slide on the first rollers; after the guiding tables slide in place, the air cylinder of the locking device is controlled to drive the rotating arm to rotate till the rotating arm is propped against the base II; and accordingly, the welding fixture can be fixed. The mechanism has the advantages that the wheels are ad