The pyrolysis gas chromatography-mass spectrometry (Py-GC-MS/MS) technique was used to study the differences in five density components of soil organic matter in alpine grassland. In this study, 150 pyrolysis products were qualitatively and quantitatively analyzed, and they were classified according to their similar chemical properties into alkyl compounds, aromatics and polyaromatics, lignin, phenols, polysaccharides, N-compounds and chitin. This study found that in alpine grassland, the F1 component, which contains compounds whose densities are less than 1.6g/cm³ were composed of plant debris. Although the percentage of this component in the whole soil was low (only 0.13%), its organic content was relatively high (5.7%). The F1 component contained more lignin and long chain alkyl compounds, which were mostly from plants, and the content of these compounds decreased gradually as the density increased. The F2 (compound densities from 1.6 to 1.8g/cm³), F3 (compound densities from 1.8 to 2g/cm³), and F4 (compound densities from 2 to 2.25g/cm³) components had similar chemical properties, and their organic compound contents showed a transition state, which increased or decreased among the density components. The F5 (compound density greater than 2.25g/cm³) component is the major part of the soil where its content is as high as 98%. The microbial polysaccharides and N-compounds (mainly from microorganisms) in the F5 component were significantly higher than in the first four components, which indicated that the F5 component contained more microbial fingerprint information. The recalcitrant substances, such as aromatics and polyaromatics, were also found in the F5 fraction.