Abstract: In general, capillary is a resistance to primary migration of hydrocarbons. Only under certain conditions can capillary pressure be effective. As regards the closed regime of capillary, gas is more easily sealed than oil. Migration stage changes with hydrocarbon generation stage. In fact, there is no fixed migration stage. It is better to make use of compaction curve in combination with geochemistry data to define the migration stage. Compaction and abnormal highpressure are closely related to each other. During migration of petroleum an important role is assigned to geopres-sure. But in practice, how to correctly understand this role and how to judge from the compaction curve stilll remain unsolved.