A new dihydroflavanoid was obtained from the root of Spiranthes australis (R. Brown) Lindl, a traditional Chinese medicinal herb. The structure was elucidated as (2S)-5,2',6'-trihydroxy-6-lavandulyl-4''-(gamma,gamma-dimethylallyl)-2'',2''-dimethylpyrano-[5'',6'' : 7,8]-flavanone by spectroscopic methods including UV, IR, HR-EI-MS, ESI-MS, 1D NMR and 2D NMR techniques, and subsequently, the anticancer activities of the compound to inhibit human cancer cells' growth including A549, BEL-7402, SGC-7901, MCF-7, HT-29, K562, and A498 cell lines by MTT method was evaluated in vitro.