Abstract: Based on the nature of macrocosm and microcosm of the cap-rock, this article systematically illustrates the relation between cap-rock and oil-gas accumulation, and its mechanism under the condition of sealing cap-rock. It is also of certain significance in the evaluation of oil-gas prospecting.

Key words: Macrocosmic nature, Microcosmic nature, Oil-gas accumlation, Oil-gas prospecting