Abstract: The South Yellow Sea Basin, as the extension of the Lower Yangtze Block to the sea, is a unified marine basin before Middle Triassic. The distribution pattern of the Triassic sedimentary facies is basically figured out on land, but the marine area remains to be researched. Referring to the researches onland, this paper is devoted to the Lower Triassic sedimentary facies of the Southern Depression of the South Yellow Sea Basin by analysis of drilling and seismic data. The results suggest that the Triassic sedimentary systems are distributed in the north-east direction of the study area where the water depth becomes shallower from northwest to southeast. Facies of platform margin slope, open platform and restricted platform successively occur along this direction. Among these facies, the dark mudstone and shaly limestone deposited in the restricted platform are the favorable source rocks. The results are meaningful to oil and gas exploration in the Triassic.