Offshore gantry lifting device with high and low legs

The utility model discloses an offshore gantry lifting device with high and low legs, and relates to the field of bridge structure component lifting and mounting devices. The lifting device comprises a low leg system, a high leg system, a truss system and a lifting system, the low leg system is positioned on a bridge floor, the high leg system is positioned in water, the truss system is positioned between the upper ends of the high and low legs, and the lifting system is positioned on the truss system. A needed component is lifted by the aid of the lifting system of the lifting device, horizontally shifted to a position above the bridge floor by the aid of a rail on a Bailey truss and movement of the lifting system and then placed on the bridge floor after reaching the height of the bridge floor, so that the mounting operation of lifting the component from a position under a bridge to the bridge floor is finished, efficiency can be effectively improved, and construction quality and safety can be ensured.