Taking the surface(0-10 cm) and deep(70-100 cm) soils from different vegetation ecosystem, i.e. tussock, shrub and primary forest as the research object in the karst area of northwestern Guangxi, China. Using pyrolysis gas chromatography-mass spectrometry(Py-GC-MS/MS) technique, we investigated the changing characteristics of soil particulate organic matter(POM) with different vegetation. The results showed that the pH value and the contents of organic carbon, total nitrogen, total phosphorus, alkali-decomposed nitrogen, available phosphorus and available potassium of surface soil all increased with the positive succession of vegetation; the contents of organic carbon, total phosphorus and alkali-hydrolyzed nitrogen of surface soil in the tussock were significantly higher than those of deep soil(P<0.05); the contents of organic carbon, total nitrogen, total phosphorus, alkali-decomposed nitrogen, available phosphorus and available potassium of surface soil in the shrub were significantly higher than those of deep soil(P<0.05), and the pH value and content of total potassium of surface soil in the shrub were significantly lower than those of deep soil(P<0.05); the contents of total phosphorus, available phosphorus and available potassium of surface soil in the primary forest were significantly higher than those of deep soil(P<0.05); along with the positive succession of vegetation, the total soil POM content increased, and the total POM content of surface soil was significantly higher than that of deep soil; the types of soil POM thermal cracking compounds mainly included lignin compounds, phenols, aromatics, polyaromatics and soil lipids, lignin compounds only existed in surface soil, and the proportion of polyaromatics (except naphthalene and indene) was a downward trend along with the positive succession of vegetation; vegetation significantly affected the total POM content and the proportions of p-hydroxyphenyl, polyaromatics, fatty acids, n-alkenes, naphthalene and cyanogens in POM thermal cracking components, soil horizon significantly affected the total POM content and the proportion of p-hydroxyphenyl, guaiacyl, syringyl, indene, fatty acid, ketones, benzene, alkylbenzene, phenols and cyanogens in POM thermal cracking components, and the interaction between vegetation and soil horizon significantly affected the proportion of p-hydroxyphenyl, terpene and fatty acids in POM thermal cracking component; the content of soil POM was significantly positively correlated with the contents of soil organic carbon, total nitrogen, total phosphorus, alkali-decomposed nitrogen, available potassium and available phosphorus, and was significantly negatively correlated with soil bulk density and the content of total potassium; the proportion of polyaromatics was significantly negative correlated with the content soil organic carbon, total nitrogen, total phosphorus, alkali-decomposed nitrogen, available phosphorus and available potassium; the content of alkali-decomposed nitrogen and pH value significant affected the proportion of POM thermal cracking compounds. Therefore, soil POM can reflect the contents of potential active nutrients in karst area soil, and can be used as a sensitive index to evaluate the impact of different vegetation restoration on soil organic matter pool and dynamic change of soil quality.