Objective A method involving derivatization combined with liquid chromatography-tandem mass spectrometry was developed for the determination of vitamin D in infant formula food.Methods The samples were treated with enzymolysis， saponification， liquid-liquid extraction， and 4-phenyl-1，2，4-triazoline-3，5-dion derivatization. Chromatographic separation was performed using an Atlantis^? T3 column， and gradient elution was performed using the methanol-5 mmol/L ammonium format solution as the mobile phase. The method applied positive electrospray ionization and multiple reaction monitoring mode and was quantified with the isotope internal standard method.Results A good linearity was obtained with a correlation coefficient above 0.99. The average recovery levels from three different ranged from 92.3% to 94.2%， and the relative standard deviations were between 3.03% and 5.34% （n=6）. The limit of quantification was 1 μg/kg.Conclusion This method is simple， accurate with high sensitivity and high selectivity， and suitable for the determination of vitamin D in infant formula food.