Based on the reflectance spectrum measured data obtained by ellipsometer, we analyse and combine the advantages of different models of smooth samples. A reflectance spectrum model for smooth samples is proposed. The different samples in various of bands are fitted, and the parameter values and the root mean square error correspondingly are analyzed. It proves that this model may fit the spectral data of smooth samples. To explore the correctness of the model, it is compared with the five-parameter bidirectional reflectance distribution function (BRDF) model. The model integration in the upper half space is compared with the measured hemispheric anti-rate data of the samples. The results show that the model satisfies both reciprocity and energy conservation law, and it could ideally replace BRDF model for smooth samples.