Abstract: The aims of this study were to find the reason of the arginine spots lag in the thin layer chromatography (TLC) identification of Ban Qing granules, and to improve this identification method. The TLC identification test was carried out as described in the current version of ChVP2015 Part Ⅱ - Ban Qing granules. Sucrose hydrolysis during TLC sample preparation process was tested by Fehling's solution. TLC sample preparation process was modified by changing the dissolution and heating steam drying methods. The results showed that the arginine spots lag in the Ban Qing granules TLC identification test was due to the Maillard reaction between arginine and the sugar reduced from sucrose during the TLC sample preparation process, and this could be eliminated by modifying TLC sample preparation process:replacing the homeopathic alcohol with 95% alcohol, and replacing the steam drying by natural volatilization drying. These results indicated that, the Maillard reaction between arginine and the reduced sugar from the sucrose in the Ban Qing granules during the TLC sample preparation, is the key reason for the arginine spots lag in TLC test. Modification of TLC sample preparation could eliminate the effect of sucrose on the TLC identification of Ban Qing granules and resolve the spot lag problem. This provides a necessary scientific basis to revise the quality standard of Ban Qing granules.