Abstarct: Calculation of the thermodynamic properties of natural gas is very important in industry. Natural gas is a complex mixture of hydrocarbons and gaseous elements such as carbon dioxide and nitrogen. Therefore, the thermodynamic properties of natural gas depend on the thermodynamic properties of its constituent elements and change with the change in natural gas composition. Using thermodynamic equations of state is one of the least expensive and fastest methods in determining thermodynamic properties. Also, to determine many thermodynamic properties such as internal energy, enthalpy, and entropy that cannot be measured by laboratory methods, we have to use equations of state. One of the most commonly used equations of state is the GERG-2008 eos, which has been studied by many researchers. The GERG-2008 equation of state is highly accurate in determining the thermodynamic properties of natural gas and taking into account the properties of natural gas components in the combination, it provides an accurate model for the calculation of thermodynamic properties such as density, enthalpy, entropy, internal energy, speed of sound and other thermodynamic properties of natural gas. In the present study, baxsed on the GERG-2008 equation of state, the thermodynamic properties of natural gas are calculated baxsed on temperature and pressure inputs and natural gas composition. Then, for validation, the obtained results obtained have been compared with the laboratory data. Also, in other thermodynamic processes such as processes in turbines, compressors and choke valves, there are other thermodynamic properties such as entropy and enthalpy, and other thermodynamic properties must be calculated from these available properties. Therefore, in this study, after calculating the thermodynamic properties of natural gas baxsed on inputs of temperature, pressure and gas composition thermodynamic properties are also calculated baxsed on three input properties models: (enthalpy, pressure and gas composition), (entropy, pressure and gas composition) and (internal energy, The specific volume and gas composition) and then the temperature drop in a choke valve and a simulated turbine are investigated. Computational validation shows that the GERG-2008 equation of state has a accuracy of less than 2%, for calculating thermodynamic properties compared to experimental data, which is very good for engineering applications. Finally, after obtaining acceptable results, to calculate thermodynamic properties of natural gas, a software is presented baxsed on GERG-2008 equation of state and four different inputs mentioned above.