Melilotus suaveolens Ledeb is a traditional medicinal plant for treating inflammation-related disease. This explores the inner anti-inflammatory mechanism of n-butanol extract from M. suaveolens Ledeb. Inflammatory cellular model was established by lipopolysaccharide intervention on RAW264.7 cell line. Levels of secreted cytokines TNF-α, IL-1β, IL-6, NO and IL-10 in supernatant, mRNA expression of TNF-α, COX-2, iNOS and HO-1, protein expression of COX-2 and HO-1, activation of NF-κB and ingredients in the extract were assayed by ELISA, real time quantitative PCR, western blot, immunocytochemical test and HPLC fingerprint test, respectively. As a result, the extract could not only markedly reduce the production of pro-inflammatory mediators to different extents by blocking NF-κB activation but also promote the release of anti-inflammatory mediator HO-1 significantly. Each 1 g extract contained 0.023531 mg coumarin and another two high polar ingredients, probably saponins. It can be concluded that the extract has similar effects on antagonizing pro-inflammatory mediators and cytokines like Dexamethasone, and has effects on promoting the production of anti-inflammatory mediators.