Abstract: In this study the blending process of Qingyan tablets was simplified and simulated, and near infrared spectroscopy was used to monitor the blending process of several raw materials in different particle size systems to explore the influence of particle size on the blending end-point. Five blended batches with different particle sizes were designed in this experiment and the near infrared spectra of the blended samples were collected. Partial least squares regression (PLSR) models of the contents of Platycodonis Radix, Fructus Chebulae, borax, Hanshuishi and microcrystalline cellulose were developed. A quantitative model was applied to determine the blending end-points of three separate batches of blends with different particle sizes. The moving block of standard deviation (MBSD) was used as a qualitative method for determination of the blending end-point. The results show that the smaller the particle size of the materials, the shorter the time to reach the blending end-points, and with more accurate model predictions. In addition, although the MBSD method is convenient and fast without modeling, the results of blending end-point determination were not as accurate as PLSR method. This approach allowed us to determine the blending end-point of Qingyan tablets.