As to the low dispersion glass H-FK61, the dispersion value is small, and its variation range is narrow, which have a very strict requirement to the measuring method. Under such circumstances, the formulae of three minimum angles of deviation are derived, and its accuracy is analyzed in comparison with traditional minimum angle of deviation method. The analysis shows that under the same condition, the accuracy of three minimum angle of deviation is higher than that of the minimum angle of deviation. Finally, we verify it at the goniometer, and solve the measuring problem of H-FK61, which lay a foundation for the measuring of another special glass FCD100.