Abstract: WO₃ thin film based on Si-NPA（WO₃/Si-NPA） was prepared by sol-gel method and spin-coating technique.The characterization of surface morphology and structure by filed-emission scanning electron microscope and X-ray diffractometer indicated that the surface of Si-NPA was well covered by a continuous layer of WO₃ thin film.By evaporating coplanar interdigital aluminum electrodes on WO₃/Si-NPA,a capacitive humidity sensor was fabricated,and humidity properties of the sensors with different thickness of WO₃ thin film were tested.It was shown that with the relative humidity（RH） changed from 11% to 95%,the capacitance of the sensor is very large and decreased with increasing testing frequency.The sensitivity of the device is strongly dependent on the thickness of WO₃ thin film,which increased sharply with increasing the thickness of WO₃ thin film,but the corresponding response time and recover time were prolonged.