Numerical analyses have been performed on a LNG(Liquefied Natural Gas) heat exchanger of the FGSS(Fuel Gas Supply System) of Hyundai Heavy Industries. A type of LNG heat exchanger currently used in FGSS is shell and tube heat exchanger which has been widely used in industrial applications. Material properties variation of the natural gas inside the heat exchanger depending on the temperature has been considered on the numerical analyses. Performance of the heat exchanger is improved by controlling baffle spacing and height, and reduction of pressure drop is verified when the baffle is rotationally periodic structure. It is because the shell-side flow is not zigzag flow but spiral flow. Although the reduction of the pressure drop results in lowering the heat transfer efficiency, it appears that if the rotational angle of baffle becomes smaller, the pressure drop decreases. Accordingly, the rotational baffle leads to higher heat transfer efficiency at the same pressure drop of a general heat exchanger with existing horizontal baffle.