Abstract: Two mini apparatus were initially made and employed for the experimental simulation of hydrocarbon gas micro-seepage through mudstone and sandstone separately. It was found out that the ratio of hydrocarbon gas components would maintain stable if they had reached the balance state in a certain sampling point and the balanced componential percentage in the total hydrocarbon was in positive correlation with the distance between sampling point and hydrocarbon resource. These characters of hydrocarbon micro-seepage have two pieces of significance: On one hand, the balance time could be calculated through experimental research or field measurement. According to the balance time, the micro-seepage velocity of hydrocarbon gas could be accounted, as well as the micro-seepage amount of hydrocarbon gas from a reservoir further according to micro-seepage model. On the other hand, through the study of the characteristics of the vertical curve of hydrocarbon componential percentage in total hydrocarbon tested from core geochemical exploration or hydrocarbon gas logging, the depth of a potential reservoir is likely to be predicted.