In the liquid level measurement principle based on acoustic resonance, level height is usually calculated via the detected fundamental resonance frequency (RF), which limits that the upper limit of measurement range is only about 8.28 m when air is a gas medium. In order to increase the measurement range, a new liquid level detector is presented using a group of RFs generated in a given frequency range instead of the single fundamental RF. The measuring accuracy of the detector can be improved by the use of error compensator based on belief rule base. This compensator enables the detector to learn compensation values from reference detection cycles; therefore, such a system is flexible and can be easily optimized under specific operating conditions. The experimental gauge is built by using low-cost components including a speaker, a microphone, a thermometer, a waveguide, a controller, and tested within a wide range with the upper limit reaching to more than 10 m. It has a better overall performance than that of the original detector.