Objective: To explore the effect of processing on the content of tetrahydropalmatine in Rhizoma Corydalis. Methods: HPLC was used with chromatographic condition included: C 18 column, mobile phase of methanol water phosphate buffer (70∶30∶1.8) and detection wavelength at UV 280nm. Results: The content of tetrahydropalmatine in the Rhizoma Corydalis processed with vinegar is the highest among all processed products. The recovery is 99.07% and RSD =1.81%, respectively. Conclusion: The processing with vinegar can increase tetrahydropalmatine content of Rhizoma Corydalis.