Abstract: A novel on-line method using high performance liquid chromatography (HPLC)with a diode array detector (DAD) and a chemiluminescence (CL) detector was successfully developed for simultaneously analyzing the antioxidant efficacies of 15 components in Guan-Xin-Ning (GXN) injection, a traditional Chinese medicinal preparation consisting of Radix Salvia miltiorrhiza and Rhizoma Ligusticum chuanxiong for the treatment of coronary heart disease and angina pectoris. The analytical conditions were optimized, validated and applied to determine H2O2 inhibition rates of the 15 phenolic acids in GXN injections from 14 different production batches. The results showed that antioxidant diversities were found in the 15 compounds and that danshensu, protocatechuic aldehyde and rosmarinic acid were largely responsible for the antioxidant activity of GXN injection (25.82%-51.19%). In addition, 14 batches of GXN injections were divided into five groups corresponding with five different factories by principal component analysis (PCA) assay. Therefore, the proposed HPLC-DAD-CL method was simple, rapid and low-cost for screening antioxidant constituents in a complex system, which can be used to reveal the antioxidant mechanism of GXN injection and is applicable for its quality control in terms of activity, which was different from the routine chemical assessment.