A new seawater salinity sensor is designed for salinity measurement by embedding the Loop resonator in MgF2 which has a positive thermo- optic coefficient. The model of seawater salinity sensor is established by COMSOL software and combining with Matlab, and characteristic parameters of the sensor are studied. The results show that the temperature characteristic of embedded ring resonator sensor depends on the microfiber radius, and the size of microfiber for weak temperature dependence decreases with the decrease of wavelength. Higher sensitivity corresponds to smaller coating thickness and smaller microfiber radius. Detection limit increases with the increase of coating thickness and decreases with the decrease of wavelength. By optimizing the parameters of the sensor, sensitivity and detection limit can reach 0.025 nm/(mg/mL) and 0.15 mg/mL, respectively.