The present invention discloses a humidity sensor and a preparation method thereof. According to the present invention, moisture-sensitive material layers are respectively arranged below, on the side surface of and above an interdigital electrode to form the structure for wrapping the interdigital electrode in the moisture-sensitive material so as to increase the volume of the moisture-sensitive material, increase the effective moisture-sensitive capacitance, and reduce the parasitic capacitance, such that the sensitivity of the humidity sensor is improved, and the performance of the sensor is improved.