Abstract: Based on the studies of relationship between the diagenesis of marine carbonate source rocks and the migration of hydrocarbons in Lower Paleozoic of Southern China, it is suggested that there are two different diagenesis, two carbonate source rocks, two different related conditions for the migration and the accumulation of oil/gas. Therefore,two different guidelines of peroleum exploraton are decided. The carbonate source rocks in basin area formed dominantly under compaction in a deep buried environment and they are the effective source rocks for the generation of oil and gas. The carbonate source rocks in platform mainly formed in cementation near surface environment. Since the lithification of such a kind of source rocks takes place before the migration of hydrocarbons, it lacks of primary migration of hydrocarbons and the source rocks are uneffcient. In this paper, it also points out that the occurrence of migrated bitumen is the key point and the evidence for the understanding of migration condition and path in those source rocks.