Abstract: OBJECTIVE To study the supercritical CO₂ extraction technique of coumarin from Melilotus officinalis (L.) Lam. METHODS The effects of extraction pressure, temperature, time and material granularity on coumarin yield were discussed by single factor and orthogonal experiment. RESULTS The influence of the factors was in order of extraction pressure > extraction temperature > extraction time. CONCLUSION The optimum extraction conditions are as follows: the extraction pressure is 25 MPa, the medicinal materials granularity is 40-60 mesh, extraction temperature is 35 ℃, extraction time is 1.0 h. In these conditions, the extraction rate of coumarin is 0.76%.