OBJECTIVE：To analyze the mass spectrometry fragmentation regularity of bicyclol ，bifendate and schisandrin C ， and to identify the impurities of bicyclol raw material. METHODS ：UHPLC-ESI-Q-TOF-MS method was adopted. Using electrospray ionization source ，in positive ion mode ，the excimer ion and characteristic fragments of bicyclol ，bifendate and schisandrin C were analyzed by means of TOF-MS. According to the mass change of fragments ，the possible fragmentation pathways were speculated ，and the fragmentation regularity were analyzed and summarized. Bicyclol raw material sample was first separated by liquid chromatography to find the impurity peaks in it ，and then the impurity peaks were analyzed by mass spectrometer；the impurity identification was conducted by combining with the fragmentation regularity. RESULTS ：The 3 compounds all produced [M+H] + excimer ion in the positive ion mode. After collision-induced dissociation ，the C-O bond ，the simple rupture of the C-C bond and the ring-opening cleavage of the oxygen ring occurred ；with the loss of neutral fragments ， mainly CH 2O，supplemented by CO 2，CO and CHO ，the dissociation was concentrated in the middle and high quality regions. C-C and C-O bonds of 3 compounds were simply broken only in the branched chain structure and/or oxygen ring structure ，but the structure of the biphenyl parent nucleus remained unchanged. Among them ，the bicyclol contained a benzyl alcohol structure ，so under acidic mobile phase conditions ，it would exist stably in the form of [M+H －H2O]+. Because schisandrin C contained 8-membered ring structure，ring opening first occurred under collision voltage ，and then neutral fragment loss occurred. The secondary mass spectra of impurity in bicyclol raw material were consistent with the mass spectra fragmentation of secondary fragments of bifendate. CONCLUSIONS：The study summarized mass spectrometry fragmentation regularity of 3 schisandrin derivatives. The impurity in bicyclol raw material may be bifendate.