Chalcone synthase (CHS) is a key and ratelimiting enzyme that catalyzes the first step in the flavonoid biosynthetic pathway. Due to the importance of these compounds, chalcone synthase gene of Caragana intermedia has been cloned and transferred into Arabidopsis thaliana and mutant tt4 and its function was analyzed. Expression of AtCHS gene in transgenic Arabidopsis was detected by qRTPCR. The total flavonoids and malondialdehyde (MDA) contents, DPPH free radical scavenging ability of transgenic Arabidopsis were analyzed by spectrophotometric method. The content of naringin in transgenic Arabidopsis was detected by HPLC method. The results showed that: (1) the expression of AtCHS gene in transgenic Arabidopsis was approximately 1/10 of wild type. Total flavonoids experimental results showed that the total flavonoids content of the transgenic lines was significantly higher than that of wild type. The naringin content in transgenic plants which was higher than that of the wild type. Accumulation of MDA before and after UV treatment in transgenic plants was significantly less than that of wild type. (2) DPPH free radical scavenging ability of transgenic plants extraction was significantly higher than that of wild type. (3) The testa of transgenic plants which CiCHS gene was complementary to Arabidopsis mutant tt4 presented a light brown color. Taken together, these results indicated that the antioxidant activity of transgenic plants was enhanced with the expression of CiCHS gene.