Because the accuracy and stability of traditional humidity sensors are easily affected by the environment, an optical fiber humidity sensor based on optical vernier effect sensitization is proposed. Two cascaded optical Fabry-Perot(F-P) interfer-ometers are obtained by successively welding a small hollow core capillary and single-mode fiber at the tail end of single-mode fiber. Adjusting the cavity length makes the spectrum range of the two interference spectrum close to each other, thus obtaining higher humidity sensitivity through the optical cursor effect. The sensing of humidity is realized by polyvinyl alcohol gel film coated on the end of the optical fiber sensing head. The experimental results show that the humidity sensitivity of the sensor based on optical vernier effect is 4.05 times higher than that of the single F-P optical fiber sensor when the relative humidity(RH) varies from 40% to 65%.