The suitability of near-infrared spectroscopy model was investigated with principal component analysis and Mahalanobis distance, and the model was modified by complementing with the samples beyond and nearby the threshold of Mahalanobis distance. Some chemical components were predicted by modified model and the average relative deviations of chlorine, potassium, total alkaloids, total petroleum ether extract, reducing sugar and total nitrogen were 7.44%, 5.33%, 3.28%, 6.94%, 3.26% and 4.65%, respectively.