LNG-FPSO(Liquefied Natural Gas-Floating Production, Storage and Offloading) is a floating vessel used by the offshore oil and gas industry for the production, processing, storage, and offloading of LNG. Since the overall production availability of an LNG plant is a major criterion for economic evaluation, it is important to have an estimation of its availability. This paper is concerned with the RAM(reliability, availability and maintainability) analysis for an LNG-FPSO gas compressor. The reliability block diagram(RBD) of the compressor is constructed by functional analysis, where the system hierarchy is classified as subunit and maintainable item. The failure rate and MTTR(mean time to repair) of maintainable items are estimated from OREDA(Offshore and Onshore Reliability Data). The failure rate and MTTR of the subunit, and the availability, failure rate and MTTR of the compressor are estimated by the PTC Windchill Quality Solution.