In the present study, mangrove Kandelia candel (L.) Druce were potted in sand and treated with different NaCl concentrations (0, 200 and 500 mmol·L^-1).The relative expression of four key genes in the flavonoid metabolism, phenylalanine ammonia lyase (PAL), cinnamic acid hydroxylase (C4H), 4pcoumaric acyl coenzyme A ligase (4CL) and chalcone synthase(CHS) were analyzed in response to salt stress by quantificational Realtime Polymerase Chain Reaction (qRTPCR). In addition, the biomass, K⁺ and Na⁺ contents, the activities of key enzymes, the contents of flavonoid and the antioxidant activity in response to salt of K. candel were investigated. Our results showed that: (1) the expression levels of PAL, 4CL, C4H and CHS were upregulated significantly under salt conditions; the activities of PAL, 4CL and C4H as well as CHS content were increased significantly with salt concentration increasing; compared with the control. (2) The plant height as well as the dry weight of leaf, root and stem were not changed significantly in NaCl treatment for 3 d and 15 d except the plant height significantly changed in 200 mmol·L^-1 NaCl treatment for 15 d. (3) The content of flavonoid, and the scavenging rate of hydroxyl radical and superoxide free radical were increased, the K⁺/Na⁺ ratio and the content of MDA were decreased significantly. These results indicate that the flavonoid metabolism in K. candel under salt conditions can be enhanced and may play an important role in the adaption to the saline environment. Accumulation of flavonoids contributes to oxidation resistance and salt tolerance of K. candel in order to maintain plant growth under salt conditions.