Abstract: Several geochemical methods to analyze light hydrocarbons in subsurface rock and soil microseeping from hydrocarbon reservoirs were set up. The hydrocarbons included adsorbed and thermally-released hydrocarbon, head space gas, and free gas, etc., but the static data analyzed through these methods could not accurately describe the occurrence states and features of microseeping hydrocarbons in the overlying strata and soil. Most past studies on the occurrence mechanism of microseeping hydrocarbons were limited to a theoretical level, and lacked the support of reliable simulation, resulting in different understandings of the application of the light hydrocarbon indexes and the independence among them, which affected the interpretation of geochemical anomalies and proper application of the methods. An experiment was conducted to simulate hydrocarbon vertical microseepage through cap rocks and overlying strata based on a simplified theoretical model of hydrocarbon microseepage. The cylinder was dissected to recover subsamples after the experiment. According to the test results of gas and rock samples, the occurrence mechanisms of free gas, head space gas, thermally-released hydrocarbon, and adsorbed hydrocarbon in the strata overlying a reservoir were studied. The results showed that the free gas indicators were best in reflecting the present features of vertical microseepage, and the adsorbed hydrocarbon indicators were not affected by gas vertical migration in the short term, whereas the thermally-released hydrocarbon indicators and the head space gas indicators were affected by gas micro-migration, with the latter being most significantly affected. Because the occurrence mechanisms and the influence factors of these hydrocarbons in rock and soil are different, the characteristics of hydrocarbon microseepage can be reflected by using these light hydrocarbon indicators from different aspects. These experiment results can help geochemical explorers deepen the understanding of different types of light hydrocarbon indicators, and to explain the geological significance of geochemical anomalies better.