Abstract: Unconformity not only plays an important role in the formation of oil and gas reservoirs,but destroys the forma-tion of oil and gas reservoirs as well. Through theoretical discussion and case studies,the destructive effects of uncon-formity towards oil and gas reservoirs have been explained in this paper. The formation of unconformity could make oil and gas reservoirs be exposed to the surface,either directly or indirectly,bringing the alteration of heavy oil (biological degradation,washing,oxidation and effusion,etc.) ,so that oil and gas reservoirs could be destroyed. Unconformity can delay or interrupt hydrocarbon generation of hydrocarbon source rocks,thereby affecting the size of oil and gas reser-voirs. Besides that,unconformity can also affect the recon-struction of sealing process of late oil and gas accumulation.