Abstract: TheMinjiang sag is the destination of Mesozoic oil and gas migration in the southern East China Sea. The formation and evolution of the sag bear great impacts on the migration, accumulation and preservation of oil and gas. Based on the seismic interpretation and balanced cross section study,it is revealed that the Yandang low uplift and Taibei low uplift had not yet formed before Late Jurassic. The Minjang sag, together with the Jilong sag in the east,accepted stable deposits of littoral facies. The faulting movement in Late Cretaceous led to the formation of the Yandang low uplift. The Oujinag sag was a typical continental fault basin filled with lacustrine deposits. The Taipei low uplift was not yet formed then. The Minjiang sag was connected with the Jilong sag to receive marine deposits as a whole.The present framework of sag sowes its origin to tectonic movements.