Abstract: The proved OOIP of Pre-Mesozoic bedrock in Damintun sag accounts for more than half of the total proved OOIP and the Pre-Mesozoic bedrock is of the uppermost oil layers.In order to make a discussion on the reasons influencing overall oil-bearing of the bedrock,namely the petroleum migration-accumulation pattern,establish the graph for various petroleum migration-accumulation pattern,and provide a guidance for Pre-Mesozoic bedrock exploration in the next step,starting from the known bedrock reservoirs,through analysis of oil property,reservoir profile,tectonic evolution,and the relationship analysis between acoustic travel time and buried depth,the crude oil type of bedrock,reservoir types and distribution characteristics have been made clear.On basis of these,the petroleum migration-accumulation conditions of Pre-Mesozoic bedrock have been analyzed in detail,and three petroleum migration-accumulation patterns,namely lateral direct pattern,vertical indirect pattern and reversed accumulation pattern,have been confirmed.The establishment of these three migration-accumulation patterns has provided important guidance for two exploratory wells in advance.