Objective A analytical method for the determination of cereulide produced by Bacillus cereus in infant formula and its arachidonic acid raw materials was developed based on online solid-phase extraction （SPE） coupled with liquid chromatography-tandem mass spectrometry. The method utilized online SPE column for purification， C18 chromatographic column for separation， and triple quadrupole mass spectrometry for detection. It was subsequently applied to the quantitative determination of the target toxin in real samples.Methods A 1.00 g test portion was weighed， and isotope-labeled internal standards were added. After the addition of 10 mL of 70% acetonitrile solution， the mixture was extracted by shaking and subjected to low-temperature centrifugation. The supernatant was filtered through a membrane， and the filtrate was purified by online SPE. Gradient elution was carried out using mobile phases consisting of 0.1% formic acid in water and 0.1% formic acid in acetonitrile. Chromatographic separation was performed on a NanoChrom ChromCore 300 C18 column （3.0 mm×100 mm， 3 μm）. Detection was conducted in electrospray positive ionization （ESI⁺） mode under multiple reaction monitoring （MRM）， and quantification was achieved using the internal standard method.Results Excellent linearity was observed over the concentration range of 0.010-5.0 μg/L， with a correlation coefficient of 0.999 9. The limit of detection and quantification were 0.030 μg/kg and 0.10 μg/kg， respectively. The average recoveries ranged from 98.5% to 106.0%， with relative standard deviations between 0.96% and 2.73%. No significant difference was observed between this method and conventional offline solid-phase extraction method.Conclusion This method is simple， sensitive， and demonstrates strong resistance to matrix interference. It can be employed as an efficient analytical tool for the food safety risk monitoring and quality control of B. cereus emetic toxin in infant formula and its raw and auxiliary materials.