Abstract: The contradiction between supply and demand caused by the rise in domestic natural gas consumption is increasingly serious. Thus LNG has been the main method of short-distance natural gas transport. While in the process of liquefying natural gas, solid phase precipitating from heavy hydrocarbon at low temperatures blocks equipment and pipeline, which causes potential security risks. To remove the peril, the gas-liquid-solid three-phase equilibrium model of the natural gas system was built and calculated. By independent research and development of the thermodynamic calculation software and the use of this model and PR equation, cyclohexane of the natural gas system in a certain area, thermodynamic data and the conditions of solid separation were carried out. By comparison with calculation results of foreign commercial software, it has shown high accuracy and could provide theoretical foundation and basic data support for natural gas liquefaction process design. Therefore, the thermodynamic model, basic data and results obtained from this research have significant theoretical meaning for the LNG industry of China.