Abstract: The potential of oil and gas resources in depositional type abnormally high pressure zone is good.All the preconditions for its existence are al- most possessed in the lower Tertiary formation in Tsiyang basin.The sealing character of abnormally high pressure zone and origin and migration of oil and gas are closely related.Sonic and seismic well logging data in 450 wells have been used to study the compaction and undercompaction characteristics in the Tertiary sediments.The results show that such data have an important value for the study of origin of the depositional type abnormally high pressure zone,as well as for the evaluation of oil-gas potential within such a zone.