The invention discloses a precise analyzer used for a tiny amount of water in oil. The precise analyzer is used for detecting water in oil stored in an oil tank, and comprises a box body, and a battery, a data processor, a power supply switch and an alarm which are arranged in the box body, wherein the power supply switch connects the battery with the data processor and the alarm respectively, various oil sample data are stored in the data processor, the data processor comparers real-time collected oil sample data with the stored oil sample data, and the data processor controls the alarm to give an alarm when the water content in the real-time collected oil sample data exceeds a standard. The precise analyzer used for a tiny amount of water in oil is movable, and allows comparison to be carried out after real-time acquisition of the data in order to realize real-time detection.