Abstract: In the conversion calculation process between the water dew point and water content of natural gas, several calculations are involved in the state equations of natural gas, gas-liquid phase equilibrium and gas mixing rules. In addition, there are many parameters are concerned and an iterative solution is required. So, the calculation is a very complex process. For these reasons, a quick and accurate calculation method for their conversion is put forward. The basic conversion process is that the PR Equation of State is used based on the incidence relation specified in GB/T 22634－2008 to calculate the fugacity coefficient about gas-liquid phase in line with the theory of phase equilibrium, and in the final, an iterative solution is used to finish the conversion calculation. Detail steps in the conversion calculation process are provided. This method is suitable for the pressure range from 0.1 MPa to 30 MPa, at -50~40 ℃. Actual calculation case shows that calculation results will be accurate if the pressure is at 0.1~5 MPa, and when the pressure is higher than 8 MPa, the uncertainty of calculation should be further analyzed.