Abstract: With the aim of assessing the dynamic evolution of marine hydrocarbon cap rocks experienced multi-cycle tectonic movements, the Paleozoic in the Tarim Basin was taken for case study. Based on the experimental test results of large amount of cap rock samples, this paper reconstructed the evolutionary process of its sealing capability by taking geological evolution as a clue and in combination with its macroscopic change, physical property evolution and stress variation. The results show that the polyphase burial changes due to uplift-depression conversion obviously controlled the sea-ling property of cap rock. Most of the Carboniferous mudstone caps had good sealing capacity in the late Hercynian in most areas except for the northwestern part where the burial depth of cap rocks was less than 2100m due to differential uplifting. Later, the sealing capacity of the Carboniferous mudstone deteriorated in the northwestern part, but enhanced in the eastern and southern parts. Salt-gypsum rocks in the Middle and Lower Cambrian established their sealing capacity in the Early Ordovician, but it became ineffective in the southwest of Yubei area where its burial depth was less than 1230m in the early Hercynian. The Carboniferous mudstone caps were regarded as the most important regional seal. Magiati slop, structural belt at the southern margin of Bachu uplift and stable area between large fault zones are the favorable areas for oil and gas preservation.

Key words: dynamic evolution, rock mechanics, cap rock, Bachu-Magaiti area, Tarim Basin