The invention relates to a large-sized lifting device positioned at the bottom portion of box girders and a method thereof, which comprises spreaders, a sling and a joist and is characterized in that the spreaders include a spreader with double hanging points and a spreader with a single hanging point, wherein the spreader with double hanging points is connected with the sling via a pin, the spreader with a single hanging point is connected with the sling via a balance plate, and the sling is connected with the joist via a neck plate and an anti-skid pin roll. The invention employs the joist and the sling to lift the box girders, simultaneously, the spreader positioned on the upper portion of the invention utilizes 'three hanging points' to guarantee the balance of the stress of hanging points, thereby not only are the safety, reliability and stability of the box girders guaranteed in the process of transporting the box girders from land to sea to be shipped, but also the invention has the advantages of skillful design, safety and reliability and easy operation.

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