OBJECTIVE：To establish a method for online detection of antioxidant active components in Glycyrrhiza uroalensis decoction pieces ，and to identify it. METHODS ：The free radical scavenging rate of 1，1-diphenyl-2-trinitrobenzene hydrazine （DPPH）was determined to evaluate the antioxidant activity of G. uralensis decoction pieces. HPLC-UV-DPPH method was used to screen the anti oxidant active components of G. uralensis decoction pieces. HPLC-TOF/MS was used to obtain mass spectrum data and Qualitive Analyst B 06.00 Build 6.0.633.0 software was used to analyze data. Through contrast analysis of UV absorption spectrum，online chromatogram ，mass spectrum information of G. uralensis and the retention time of each compound ，accurate molecular weight ，antioxidant active components were identified by referring to relevant literature. Validation test was also conducted. RESULTS ：DPPH free radical scavenging rate in 8 batches of G. uralensis decoction pieces ranged 55.71％-60.17％. Seven antioxidative active compounds ，including avolomotor ，8-isopentenyl naringin ，yellow lupulin weitone ，isoflavone B ，3′， 4′-dimethoxy3-hydroxy-6-methyl flavone ，glycyrrhizin E and glycyrrhizin H ，could be screened from G. uralensis decoction pieces. After validation ，the peak area of inverted peak generated by online reaction was positively correlated with DPPH free radical scavenging rate. CONCLUSIONS ：Established method is simple and accurate ，and can be used to quickly screen and identify the main antioxidant components of G. uralensis decoction pieces ；the peak area of inverted peak can be used to evaluate the antioxidant active components of G. uralensis decoction pieces.