The invention discloses a salt density sensing element and a salt density sensor. The salt density sensing element is of optical fiber gratings the reflection wavelength of which changes as the density of salt water changes, and the salt density sensor consists of the salt density sensing element, a broadband light source, an optical fiber coupler and a quasi-distributed optical fiber grating demodulation system. The salt density sensor provided by the invention can be used for monitoring the equivalent salt density of sea water. The salt density sensor provided by the invention has the characteristics of high sensitivity, good stability, simple structure, small volume, light weight, convenient installation and low cost.