A new automated dewgauge is proposed. It consists of CCD image sensor, dew collector and processor, in which dew collector comprises three set glasses installed at different height, and each glass set consists of transparent glass and ground glass. The brightness of the glass would change when condensation occurs. The images of three set glasses are transmitted to the processor to determine whether moisture condensation occurs. The humidity is measured using hygrothermograph to test the dew automated data. Research has shown that it is possible to discriminate the moisture condensation. The normalized brightness difference of the glass decreases rapidly when the relative humidity is greater than 97.9%. The measured method and the algorithm have good performance. The dew acquisition can be a hundred percent and the automatic identification rate arrives more than 85%. Thus it can be applied to meteorological observation.