This paper presents a new intelligent moisture controlling system based on the resistance sensor for molding sand. A kind of moisture sensor with high sensitivity, simple structure and being suitable for on-line detecting is designed. A moisture measuring circuit founded on integrated method of frequency and period measuring is proposed. The circuit translates the relation between the sensor’s resistance variation and moisture into that of frequency and moisture, which makes the system to be capable of wide measurement range and high measurement accuracy. What’s more, the system has the features of strong ability of anti-interference and adaptation to remote measuring. Testing result shows that the moisture measuring and controlling accuracy of the proposed system can achieved ±0.2%.