Dependence of refractive index (RI) of seawater on salinity, temperature and wavelength n (S, T, λ) in infrared band is required.However, almost all the existing empirical formulas of the RI of seawater are suitable for the visible waveband (400 nm - 700 nm). There is little report on developing the RI expression of seawater in infrared band, especially the most commonly used 1200 nm - 1650 nm waveband.