In order to measure the stress-induced birefringence and optical homogeneity of fused silica，a method of proportioning refractive index fluid is put forward. Firstly, according to the characteristic of the groups in molecules and molar refraction additivity of the two solutions, formulas for the refractivity of binary solution are analyzed and the technique is given. Secondly, dependence of the refractive index of fluid on different temperatures and wavelengths, is analyzed and verified experimentally. At last, the influence of refractive index fluid precision on test result is analyzed. According to the method, the match precision of the fluid and fused silica can be ±2×10-5; Through the experiment of rough-ground glass, the fluid can improve the transmission from below 20% to above 97% at the wavelength between 450 nm and 700 nm. The fluid which is prepared by the method and the composition we choose, has the characters of low toxicity, no color, no smell, nonvolatile, and its refractivity can remain stable for long. It can be well used for the measurement of the stress induced birefringence and optical homogeneity.