Magnetic flap level gauge can be used for medium level detection of various towers, tanks, spherical vessels and boilers. This series of magnetic level gauges can achieve high sealing, anti-leakage and high pressure and high temperature, under corrosive conditions. The liquid level measurement has reliable safety, which makes up for the lack of clear indication of the glass plate (tube) level gauge, easy to break, is not affected by the high and low temperature drastic changes, and does not require the combination of multiple sets of liquid level gauges. The whole process measurement has no blind zone, the display is eye-catching, the reading is intuitive, and the measuring range is large, especially the on-site indication part. Because it is not in direct contact with the liquid medium, it is more sensitive to high temperature, high pressure, high viscosity, toxic and harmful, strong corrosive medium. Its superiority, therefore, it has higher reliability, safety, advancement and practicability than traditional glass tubes and plate level gauges.