Abstract: The volatile components of Cajanus cajan roots were studied, as well as the biological functions of volatile components of Cajanus cajan roots, to provide a scientific basis for the development and utilization of volatile components of Cajanus cajan roots. The volatile components of Cajanus cajan roots extracted by steam distillation were detected by headspace extraction-gas chromatography-mass spectrometry（HS-GC-MS）. The results indicated that: A total of 98 volatile components were identified from the roots of Cajanus cajan, including alcohols, esters, aldehydes, ketones, acids, terpenes, alkanes, aromatics and alkaloids. Among them, terpenes had the largest number with 47 and the highest relative content with 77.863%. The higher volatile components in Cajanus cajan roots were 10s,11s-Himachala-3（12）,4-diene,（+）-β-Himachalene, Di-epi-.alpha.-cedrene, α-himachalene, cis-（−）-2,4a,5,6,9a-Hexahydro-3,5,5,9-tetramethyl（1H）benzocycloheptene, whose relative contents were 11.377%, 10.289%, 7.564%, 5.834% and 5.804%, respectively. It is believed that the volatile components of Cajanus cajan roots play an important role in resisting bacteria and insects infestation and inhibiting weeds.