Abstract: The dynamic changes of six phenolic acids contents were evaluated by using high performance liquid chromatography-mass spectrometry during vitro rooting process of three cultivars (‘Wu Long Peng Sheng’, ‘Tai Ping Hong’, ‘Feng Dan Bai’ ) in order to research the relationship between phenolic acids and the occurrence of adventitious roots in tree peony (Paeonia suffruticosa Andr.). Results showed that six phenolic acids contents varied with time in different amplitude during the vitro rooting process. However, they were difference in the dynamic changes among the three tree peony cultivars. Paeoniflorin, benzoic acid and 4-hydroxy benzoic acid contents were higher in easy-to-root ‘Tai Ping Hong’ cultivar than in difficult-to-root ‘Feng Dan Bai’ and ‘Wu Long Peng Sheng’ cultivars, while methyl gallate and shikimic acid contents were lower in ‘Tai Ping Hong’ than in ‘Feng Dan Bai’ and ‘Wu Long Peng Sheng’. However, no clear conclusions could be drawn for gallic acid content in correlation to the rooting ability of the three tree peony cultivars. The results held that paeoniflorin, benzoic acid, 4-hydroxy benzoic acid, methyl gallate and shikimic acid were closely related to the rooting of tree peony, the influence of gallic acid in rooting was little.