Abstract: A UPCC-Q-TOF-MS method was established to analyze the components of polyoxyethylene 35 castor oil. The separation was performed at 50℃ on a Waters Acquity UPCC system by an Torus Diol column (3.0 mm×100 mm, 1.7 μm) with gradient elution of CO₂ and methanol-acetonitrile (50:50); the flow rate was 1.0 mL·min^-1, the back pressure was 2 000 psi, and methanol containing 2.5 mmol·L^-1 ammonium formate was used as ionization reagent, whose flow rate was 0.2 mL·min^-1. Positive ion electrospray ionization (ESI) mode and MS^E technology were used. The qualitative analyses were carried out by using precise mass information of the parent and product ions and a PCA model was established by UPCC-Q-TOF-MS. L-02 cells and RBL-2H3 cells were used to study the cytotoxicity and histamine release of CrEL samples in vitro. A total of 13 kinds of CrEL components were obtained and their structures were identified by UPCC-Q-TOF-MS, with 255 compounds in total. The percentage content of 13 types of components was calculated by the normalization method. The content of polyoxyethylene glycerol tri-ricinoleate (PGTri-ricinoleate) in all samples was 0.36%-2.80% and the main components were polyethylene glycol, polyethylene glycerol and polyoxyethylene glycerol mono-ricinoleate. All samples have different degrees of cytotoxicity and histamine release, which is negatively correlated with the content of PGTri-ricinoleate and positively correlated with the content of polyoxyethylene glycol fatty acid esters. The UPCC-Q-TOF-MS method is simple and rapid, has strong separation ability and high accuracy. It is suitable for the analysis of CrEL components. It is suggested that the fatty acid composition should be included in the monograph of CrEL for injection to increase the content of PGTri-ricinoleate and decrease the content of polyoxyethylene glycol fatty acid esters, so as to improve the product safety.