Oil is the most dominant source of energy in the global energy market over the past decades but the global energy market structure has been changing sharply because of environmental restrictions. Natural gas is a clean source of energy and is preferred because it offers a number of significant environmental benefits against other fossil fuels such as oil and coal. Pipelines remain the dominant method of transportation of natural gas, because the large volume necessary for use makes most other forms of transportation too costly. Another method of transporting natural gas is to be compressed, refrigerated and supplied as a liquid known as liquefied natural gas(LNG). When there is a considerable distance involved in transporting natural gas, LNG is the preferred method of natural gas supply because of technical, economic, safety and political reasons. Therefore, LNG is expected to play a major role as a clean energy. The global use of LNG is increasing sharply. Worldwide LNG demands expand from 159 million ton in 2006 to 500 million ton in 2030, achieving 3.6-fold growth. This study focuses on the design of liquefaction process in LNG plant. The simulation and optimization of the liquefaction process are carried out to obtain the improved process design for energy saving. The optimal design of processes requires less power and cost at given specific plant capacity. Designing cost-effective process of high efficiency becomes a key contribution for optimal LNG plant. The conditions and configurations of liquefaction process are suggested in comparison with several commercial liquefaction processes. An efficient natural gas liquefaction process is developed in this research. This research was supported by a grant from the GAS Plant R&D Center funded by the Ministry of Land, Transportation and Maritime Affairs (MLTM) of the Korean government.