Salinity is one of the most important parameters in oceanography. The study of high-precision measurement technology of ocean salinity has far-reaching significance for revealing the influence of distribution and change of ocean salinity on ocean dynamics and global change. Dissolved silicate (DSi) is an important nutrient in the hydrosphere and an important component of seawater salinity, and the influence of its content on absolute salinity should not be ignored. However, the contribution of silicate to the conductivity is not significant, and the traditional conductivity sensor can not accurately perceive its content. To obtain high precision ocean salinity data, it is necessary to understand the influence of dissolved silicate concentration on the measurement results of seawater refractive index, electrical conductivity and salinity.Based on the principle of optical refraction, a new type of measurement system for seawater refractive index with V-shaped groove is established. The system uses a high-performance CMOS camera module as a position sensor to measure the refractive index and salinity of seawater by accurately measuring the tiny position changes of the light emitted from the V-shaped groove. The resolution of the system is 2.45×10^-7 RIU, and the measurement range is not less than 36 000 points. Based on the measurement of refractive index of Chinese standard seawater with different concentrations of sodium silicate (salinity is (35±0.003) PSU), the effects of silicate on the measurement results of refractive index and salinity were studied, and the effects of dissolved silicate on the measurement results of refractive index, conductivity and salinity of seawater were compared with the traditional measurement results.The experimental results show that the refractive index contribution of sodium silicate seawater can be effectively reflected by optical refraction method. At 25 ℃, the refractive index of (35.000±0.003) PSU standard seawater linearly increases by 1.62×10^-4 RIU with 1 g/kg increase of sodium silicate concentration, and the corresponding practical salinity increases by 0.907 PSU and absolute salinity increases by 0.911 g/kg. However, the contribution of sodium silicate to the conductivity of seawater is not obvious, but due to the polarization effect, with the increase of sodium silicate concentration, the statistical decline of the conductivity measurement results is caused by the increase of sodium silicate concentration of 1 g/kg, resulting in a decrease of 0.054 mS/cm in the conductivity measurement results, and the corresponding practical salinity is 0.054 PSU. The difference between the two methods is 0.961 PSU, and the corresponding absolute salinity is 0.966 g/kg, which is close to the concentration change of sodium silicate.When the silicate concentration is higher than 0.001 g/kg, the contribution of silicate to seawater salinity can be effectively reflected by optical refraction method. When the silicate concentration is low, the refractive index resolution of the optical system needs to be further improved. Compared with conductivity measurement, optical refraction method has a wider range of material measurement, and can sense the existence of conductive and non-conductive substances in seawater.