The principal refractive indices of BIBO crystal for wavelengths of 0.4880,0.6328,1.0640 and 1.3414 μm under the temperature range from 30℃ to 170℃ were measured by auto-collimation method.The Sellmeir-equations at different temperatures and thermal coefficients of refractive indices have been obtained. In order to check their reliability,the refractive indices of 1.0795 μm in different temperatures are calculated by the Sellmeir-equation and then compared with the measured values. As a result,the difference between the calculated results and the measured results is less than 2×10^－4.