In order to apply the fiber reinforced plastic(FRP) to support panel of polyurethane foam in LNG storage tank, we estimated the mechanical properties, degree of vapour barrier, chemical stability and thermal conductivity changes as ageing. According to the results, the mechanical strength (compressive strength, bending strength, tensile strength and shear strength) are more than 30 times higher than mechanical properties of plywood. The FRP-polyurethane foam(PUF) composites have lower thermal conductivity changes as ageing than plywood-PUF composites. FRP-PUF sandwich composite for LNG storage tank with these remarkable properties, are compared the abilities of these structures with those of the conventional structures(plywood-PUF sandwich composite), so we can obtain the effects such as superior mechanical properties and fuel saving through improved ability of vapor barrier.