The invention relates to a box body assembling system and method of a polyurethane insulation box for liquefied natural gas (LNG) ships. The box body assembling system of the polyurethane insulation box for liquefied natural gas (LNG) ships comprises a base, an X-direction positioning and correcting mechanism, a Y-direction positioning and correcting mechanism and a wood clamping-plate correctingmechanism, wherein the X-direction positioning and correcting mechanism, the Y-direction positioning and correcting mechanism and the wood clamping-plate correcting mechanism are separately arranged on the base. During assembling, the X-direction positioning and correcting mechanism and the Y-direction positioning and correcting mechanism are used for positioning and correcting the X-direction andY-direction of the polyurethane insulation box, and a wood clamping-plate is tightly pressed by the wood clamping-plate correcting mechanism. Compared with the prior art, the box assembling precisionof a plurality of modes of NO.96L03/L03+ series enhanced polyurethane standard insulation boxes can be controlled, the assembling precision requirements under different production conditions can be met, the operation is simple and convenient, and good product quality consistency is achieved.