OBJECTIVE To improve the quality evaluation method of Platycodonis Radix, to study the differences in the quality of three-years-old Platycodonis Radix under different harvesting periods, and to determine the optimal harvesting period of Platycodonis Radix. METHODS The leachate, ash, moisture, refractive index and the content of six saponins were used as the quality evaluation indexes. The differences between the herbs of Platycodonis Radix at different harvesting periods were characterized with the help of mathematical and statistical methods. And link the entropy weight method, gray correlation analysis and TOPSIS method were combined to obtain the statistical analysis of the relevant indexes and the quality ranking information of the herbs in different harvesting periods. RESULTS There were significant differences between the quality evaluation indexes of three-years-old Platycodonis Radix at different harvesting periods. The added multi-indicator testing had improved the quality evaluation system of Platycodonis Radix and enhanced the "Drug properties-Effectiveness" linkage of the herbs. And the results of the comprehensive quality evaluation model showed that the herbs harvested around October 21 (Frost’s Descent) were ranked best in terms of comprehensive index. CONCLUSION In order to ensure the quality of Platycodonis Radix, the best harvesting period for three-years-old Platycodonis Radix is determined around the "Frost’s Descent" season, taking into account the characteristics of the herbs' appearance and the material basis of herbs.