Inttroduction Liquefaction natural gas, shortly called LNG, is condensing natural gas into liquid by cooling the gaseous natural gas under normal pressure to – 162 ℃. Natural gas liquefaction can greatly save storage and transportation space, and has the advantages of large calorific value, high performance, conducive to the balance of urban load regulation, conducive to environmental protection, reducing urban pollution and so on. Liquefaction is the core of LNG production and skid mounted LNG plant. At present, the mature natural gas liquefaction processes mainly include cascade liquefaction process, mixed refrigerant liquefaction process and liquefaction process with expander. Cascade natural gas liquefaction process uses different boiling points of refrigerant under normal pressure to reduce the refrigeration temperature step by step to achieve the purpose of natural gas liquefaction. Mixed refrigerant cycle (MRC) is a process in which more than five kinds of multi-component mixed refrigerants, such as C1 ~ C5 Hydrocarbons and N2, are used as working fluids to condense, evaporate and expand step by step to obtain refrigeration capacity at different temperature levels, and then gradually cool and liquefy natural gas. Mixed refrigerant liquefaction process is divided into many different types of refrigeration cycle. The liquefaction process with expander refers to the process of natural gas liquefaction by using high pressure refrigerant to realize reverse Claude cycle refrigeration with adiabatic expansion of turbo expander. The process scheme mainly includes: feed gas pressure regulating and metering unit, natural gas purification unit and natural gas liquefaction unit, refrigerant storage system, refrigerant circulating compression system, LNG storage and loading unit.  Design parameter To design a LNG Plant Skid, we need the following parameter. 1) Basic conditions of plant design: Feed gas flow Feed gas pressure Feed gas temperature Free water content of feed gas   2）Detailed feed gas composition (mole%)   3) Product specifications： Liquefied natural gas: Outlet pressure Subcooling temperature under outlet pressure Maximum nitrogen content Maximum carbon dioxide content