A high-performance liquid chromatography tandem mass spectrometric(LC-MS/MS) method was developed for the determination of histamine in the supernatant after degranulation of P815 cells．After pretreatment procedure,the sample was separated on a C18(4.6 mm × 100 mm，3.5 μm) column using acetonitrile-0.5 mmol/L ammonium acetate solution with 0.3% formic acid(60∶40) as mobile phase at a flow rate of 0.4 mL/min.The target compound was detected by positive ion ionization mass spectrometry(ESI MS) under multiple reaction monitoring(MRM) mode using m/z 112＞95 and m/z 112＞68 as detection ion.Under the optimal conditions,the analysis of sample could be completed within 6 min.A good linear relationship was obtained for histamine in the range of 4.0-128.0 μg/L with a correlation coefficient(r2) of 0.997 9.The limit of quantitation(S/N＞10) and limit of detection(S/N=3) were 1.2 μg/L and 0.3 μg/L,respectively.The mean recoveries for histamine in the supernatant of cells at three spiked concentration levels of 16,64,128 μg/L were in the range of 90%-94% with relative standard deviations(RSDs,n=6) of 4.1%-5.9%.The proposed method was simple,sensitive and reproducible,and was suitable for the determination of histamin in the supernatant of Traditional Chinese Medicine Injection(TCMI) on degranulation in P815 cells.