The rules of quartz crystal that the refractive index varies with the wavelength at different temperature are studied. With strict solution,the expression about the coefficient of Sellmeier equation is gained,and the refractive indices corresponding to different wavelength are calculated,they are consistent with the experimental results . The expression of the thermal refractive index coefficients at different wavelength are gotten by curve-fitting means,and the thermal refractive index coefficients at different wavelength are calculated. Then the constants of the Sellmeier equation at different temperature are gained,so a method of doing the refractive indices of quartz crystal at different temperature and different wavelength is got.