A Fabry-Perot Interferometer (FPI) was constructed by fusion splicing a Hollow Core Fiber (HCF) with a length of tens of microns at the end of a single-mode fiber and coating gelatin film at the free end of the HCF. Relative humidity measurement was achieved by detecting wavelength shift of the interference spectrum with humidity level changes. Experimental results show that high sensitivity of 192 pm/%RH has been obtained in the temperature range of 20 ℃ within the range of 20%~80%RH and the measurement accuracy and repeatability are quite good. In addition, the sensitivity of 173 pm/%RH and 194 pm/%RH were obtained by humidity increasing experiments at 15 ℃ and 25 ℃, respectively. In order to measure temperature has also been achieved by cascading a fiber Bragg grating sensor with the FPI sensor head. The optical fiber humidity sensor possesses several advantages including simple fabrication, high sensitivity, and temperature measurement. It has good potential in the field of humidity measurement.