This paper presents a detailed study on relative humidity sensor based on distributed fiber Bragg grating(FBG) coated with polyimide(PI) as a moisture sensitive film.The wet expansion of PI film as wet strain on the FBG results in the shift of Bragg wavelength.The sensor realizes the relative humidity monitoring of 26%RH-98%RH.The method achieves FBG humidity sensor′s better performance by improving the preparation and coating process of PI film and also compensates the temperature.On this basis,the distributed optical fiber Bragg humidity sensor system is prposed for the requirement of multi-point humidity monitoring.The experiments prove that the method can effectively improve the sensor performance,the humidity sensitivity of the sensor is 15 pm/% RH and the linearity error is less than 2.75%.The sensor also has good repeatability and stability.