Color characterization of display was studied by using polynomial regression and spectrum analysis. Once fitting and twice fitting between the RGB signals and the L*a*b* values were applied to establish color space conversion model. Through comparing the difference of ΔE and σ2, the differences of the models were analyzed. The results showed that the model can get satisfactory result when number of terms is 9 and 11; twice fitting is better than once fitting; when the term is 20, the model is not stable.