OBJECTIVE：To study the co rrelation of the chro maticity value of Schizonepeta tenuifolia charcoal of different processing time（0-40 min，similarly herein after）with multiple indicators ，and to reveal the quality change law of S. tenuifolia charcoal during processing and confirm the terminal time. METHODS ：The contents of ethanol-soluble extracts from S. tenuifolia charcoal decoction pieces of different processing time were determined. UPLC fingerprint of S. tenuifolia decoction pieces and S. tenuifolia charcoal decoction pieces of different processing time were established ，and the similarity evaluation was also conducted. The chromatographic peaks were confirmed by comparison with substance control. The same UPLC conditions were used to determine the contents of index components （hesperidin，rosmarinic acid ，menthone）in S. tenuifolia charcoal decoction pieces of different processing time. The colorimetric method was used to measure the chromaticity value of S. tenuifolia charcoal decoction pieces of different processing time. Meanwhile ，sample of processing 0 min was used as a control to calculate the total color value （E）and the total color difference value （ΔE）. Pearson correlation analysis ，cluster analysis and orthogonal partial least squares discriminant analysis （OPLS-DA）were performed on the ethanol-soluble extracts ，index component contents ，chromatographic peak area and chromaticity value. The terminal time of processing S. tenuifolia charcoal was conf irmed，and validation test was also conducted. RESULTS ：With the extension of processing time ， the content of ethanol-soluble extract in S. tenuifolia charcoal qq.com decoction pieces gradually decreased. A total of 17 chromato- graphic peaks were identified in 12 batches of S. tenuifolia decoction piece ，and its si milarity with the control fingerprint was greater than 0.9. 21 chromatographic peaks were identified in S. tenuifolia charcoal decoction pieces of different processing time，and its similarity with the chromatogram of sample of processing 0 min decreased with the processing time ，and the similarity after 18 min was lower than 0.9. The chromatographic peak 9 was hesperidin ，peak 10 was rosmarinic acid and peak 17 was menthone. The determination of content and chromaticity value showed that with the extension of processing time ，the contents of hesperidin ，rosmarinic acid and menthone decreased gradually ；the color L，b and E values of S. tenuifolia charcoal decoction piece powder decreased gradually ，and the a and ΔE values increased gradually. Pearson correlation analysis showed that the contents of ethanol-soluble extract ，hesperidin，rosmarinic acid and menthone ，the peak areas of 15 chromatographic peaks （peak 2，7-15，17-21）were significantly positively correlated with E value（P＜0.01）；the peak areas of 5 chromatographic peaks （peak 1，3-6）were significantly negatively correlated with E value（P＜0.01），but peak area of peak 16 was not related to E value（P＞ 0.05）. Results of cluster analysis showed that S. tenuifolia charcoal decoction pieces of different processing time were divided into 2 categories；the first category was processed for 0-16 min，and the second category was processed for 18-40 min. The results of OPLS-DA showed that the VIP values of peak 6 area（2.800 75），L value（2.327 54），peak 3 area（1.793 39），b value（1.735 78） and peak 5 area（1.244 04）were greater than 1. The final processing time of S. tenuifolia charcoal was 18 min. The results of validation experiment showed that the L，a and b values of S. tenuifolia charcoal decoction piece were 20.22-22.00，4.44-7.67， 9.78-13.00，and ΔE were 13.50-14.12，respectively. CONCLUSIONS ：The chromaticity value of S. tenuifolia charcoal decoction pieces of different processing time is closely related to the contents of ethanol-soluble extract ，hesperidin，rosmarinic acid ， menthone and the area of 20 chromatographic peaks. It is suggested that the terminal time of processing S. tenuifolia is 18 min.