Abstract: The change of air relative humidity will cause the small change of the induced capacitance of the environment.For high quality factor resonant circuit，in its resonant state，the capacitance of small changes will lead to significant changes in signal amplitude. Using these characteristics，a measuring device is designed to obtain the relative humidity of air according to the change of signal amplitude. The device has simple structure，high precision，rapid reaction，can be used in teaching and demonstration and has high commercial promotion value.

Key words: air relative humidity, micro capacitance measurement, resonant circuit