The air humidity is one of basic elements of ground and upper air meteorological observation. In order to design a dew point type hygrometer for meteorological business, this article introduce a condensationtype humidity sensor which is infused with microscopic optics, image recognition, embedded system and automatic control technology. After computing and simulation, the sensor is successfully designed based on the principle of condensation method. Mainly key technologies such as condensation mirror design, temperature control, condense identification algorithm and so on are solved. Then static and dynamic test with humidity standard device MBW373 and humidity sensor HMP155a are carried out separately in different conditions. The test results shows that the prototype has good consistency with both contrasts, the deviation of relative humidity with the standard device is between -2.86%RH and -0.95%RH, the mean error is -1.66%RH which meet the business application of ground meteorological observation.