Abstract: Natural gas viscosity is one of the important basic physical property parameters in the design of oil production and surface gathering and transportation technology. In the exploration of a gas field, there is significant variation in the composition of wellbore gas, and the presence of heavy components and non-hydrocarbon CO₂ generally increases the gas viscosity. Therefore, the main factors affecting viscosity were discussed by experimental analysis. Based on the experimental data, ASPEN HYSYS software was used to evaluate the predictive accuracy of 10 state equations such as PR and SRK on viscosity. The results indicate that pressure, temperature, and gas composition are significant factors affecting the viscosity of natural gas samples, among which pressure and the content of heavy hydrocarbon components in gas components have great influence on viscosity. Under the same temperature condition with the increase of pressure, the viscosity of the gas increases gradually. Under the same pressure condition with the increase of temperature, the viscosity of the gas gradually decreases. When the pressure is less than 20 MPa, the effect of temperature on gas viscosity can be neglected. The average relative error and maximum relative error of the SRK state equation are both minimum, which is the preferred method for calculating the viscosity of natural gas in the gas field and can meet the requirements for surface engineering design.