Abstract: A method for the rapid determination of 5 '- inosinic acid and 5' - guanosine acid in yak meat by ultra high performance liquid chromatography couple with tandem mass spectrometry (UHPLC-QTOF-MS) was established. Firstly, the extraction process of ionosine-5'-mono-phosphate (IMP) and guanosine-5-monophosphate (GMP) was optimized by orthogonal test, and then the qualitative and quantitative analysis of IMP and GMP was carried out by UHPLC-QTOF-MS. The results show that the linear relationship between 5' -inosinic acid and 5' -guyanic acid is good within the mass concentration range of 0.312 5~50.0 g/mL, and the average recovery is 101.53% and 96.27%, respectively, and the | matrix effect | is 26.21% and 16.27%, respectively. This method has the advantages of high efficiency, fast detection, high sensitivity and good reproducibility. It can provide technical support for the study of flavored nucleotides in yak meat.