In order to promote the application of high-temperature and pressure steam relative humidity measurement in industrial production and widely develop the traceability of the International System of Units (SI) of relative humidity above 100℃, this article summarizes the latest research on the preparation for standard humidity of high-temperature steam, the principle of relative humidity measurement technology and the corresponding measurement range. The measurement deviation and uncertainty between different methods were compared through comparative measurement, and a comprehensive analysis was conducted based on the traceability for relative humidity measurement and the technology characteristics. The comparative experiment shows that under the dew point temperature of 127℃, the test deviation between the steam expansion method and the microwave resonance method gradually increases with the increase of relative humidity. When the relative humidity reaches 70%, the deviation is close to 4%. Under the condition of dew point temperature of 128℃ and relative humidity of 95%, the test deviation and uncertainty between steam condensation method and gas-steam mixing method are not exceed 0.5% and 1%. The four measurement methods can effectively measure the relative humidity of high temperature and pressure steam with the dew point temperature above 100℃.