The utility model discloses an oil tank moisture detecting device, including the little water rigorous analysis appearance of probe rod and oil, because there is the drain oil tank bottom, the sample connection, a plurality of outer mouths that ally oneself with such as oil -out, because movable is chooseed promptly for use to the design original intention of probe rod, so it is feasible to occupy one of them mouthful entry that the spy is gone into as the sensor, so when using, the water changer that at first will decline is connected with data collection facility so that subsequent data transmission, then data collection can in sending the moisture inductive pick -up into the oil tank through the body is direct, oil appearance data transfer to the data processor that little water changer will be gathered, the little water rigorous analysis appearance of oil is movable, contrast after can real -time data collection, the inside storage of data processor has multiple oil appearance data, data processor compares real -time collection's oil appearance data with the multiple oil appearance data of inside storage, when moisture exceeds standard in real -time collection's oil appearance data, data processor control alarm is reported to the police, realize the real -time detection.