Abstract: Seawater intrusion is a major disaster that cannot be ignored in coastal areas,which will lead to water quality deterioration,soil salinization and other problems. Therefore,in-situ and real-time monitoring of groundwater salinity is of great significance. In this paper,a salinity sensor based on the filtering characteristic of Fiber Bragg's Grating(FBG)was proposed. The fiber cladding was corroded by chemical corrosion to make FBG sensitive to the external refractive index,so as to realize salinity sensing. The relationship between the central wavelength and salinity of FBG with different corrosion degrees was simulated by MATLAB software,and the theoretical feasibility of this method was verified. At the same time,the temperature and salinity sensitivity of EFBG(Etched Fiber Bragg grating) was tested separately,and an uncorroded FBG was introduced for temperature compensation to achieve the simultaneous measurement of salinity and temperature. The experimental results show that the wavelength drift of EFBG with different corrosion degrees has a linear relationship with salinity. The higher the corrosion degree in a certain range,the greater the salinity sensitivity coefficient,up to 29.432 pm/%,which proves that EFBG has a certain feasibility for seawater salinity measurement. Finally,an encapsulation method for in-situ monitoring of groundwater salinity is proposed,which provides a new measurement method for the study of seawater intrusion in coastal areas.