The utility model relates to a be used for hoist girder roof beam case welded clamping device, moreover, the steam generator is simple in structure, and convenient for operation, at first adjust hydraulic cylinder to appropriate position through the regulating action of pin and jack, to form and carry out earlier simple spot welding between the steel sheet of roof beam case and handle, then the roof beam case that will treat welding process is put between two end plates that the clamp is tight, the starter motor drives hydraulic power unit and supplies hydraulic oil for hydraulic cylinder, hydraulic cylinder's tailpiece of the piston rod stretches out, driving terminal board clamped beam case, the backup pad moves to the roof beam case in the through -hole simultaneously, hydraulic cylinder's the first spring of stiff end compression, at the in -process of backup pad to the removal of roof beam case, the fixed plate is along the guide bar to cardboard rectilinear movement, fixed platecompression second spring, guarantee the stationarity of hydraulic cylinder at clamped beam case in -process, treat that the roof beam clamp can carry out welding operation by the coupled beam case after tight, guarantee roof beam case welded quality, weld effectually.