In order to make better use of the tunable properties of magnetohydrod ynamic refractive index,optical devices such as magnetohydrodynamic grating,magnetohydrodynamic fiber modulator and magnetic field sensor are designed.Through theoretical analysis,this paper studies the tunability of magnetohydrodynamic refractive index from three factors of magnetic field size,direction and temperature.Based on Fresnel reflection theory,a miniature closed reflection sensor is designed to measure the refractive index o f magnetic fluid.The known sample calibration method was used to solve the interference problem of the system′s i ntrinsic reflection.The magnetic field intensity,the Angle between the sensor and the magnetic field and the tem perature were adjusted respectively. The refractive index of magnetic fluid was measured.Results show that under the effect of magnetic field,the magnetic liquid refractive index in the beam direction of electric and magnetic fields at different angles,magnetic liquid refractive index with the magnetic field strength increase and present a trend of increasing and decreasing, increasing trend,the most obvious when the parallel magnetic liquid refractive index changes in 0.017,when the vertical downward trend,the most obvious magnetic liquid refractive index chang e 0.0152;At the same time,a cubic polynomial equation with refractive index and temperature fit of 0.98997is obtained.The results are of great significance to the structural design of magnetohydrodynamic optical devices.