In a high-temperature gas-cooled reactor, the coolant within the primary loop is helium. The humidity level of the helium in the primary loop, which functions as the alarm and protection trigger signal in the event of a steam generator pipe rupture accident, represents a crucial parameter for ensuring the safe and reliable operation of the reactor. Owing to the inferior reliability of the analog circuit transmitter, the lifespan of the dewpoint instrument utilized in the HTR-PM is merely one year. Moreover, there is a pressing need for further enhancement in terms of its measurement precision and maintainability. This paper delineates the R&D status of a long-service-life, high-precision, fully domestically produced, digital Class 1E dewpoint instrument, includes design schemes, test items and test results, etc.