A systematic study on the vertical and horizontal distributions of the thickness and the organic matter abundance for four suites of Paleozoic regional marine source rocks(〗〗3—S1，P1 and P2 ) has been made by geochemical analyses on the source rock samples from 98 outcrop profiles and 23 well profiles in Upper, Middle and Lower Yangtse River regions. It is clarified that in vertical the Lower Cambrian and Upper Permian source rocks are the best, and in horizontal the source rocks in Upper Yangtse River regions are the best and then those in Lower Yangtse River are the secondary, respectively. Five developmental source rocks areas are defined. It has shown that marine source rocks are predominated by mudstones in these areas and carbonate source rock occurs only in the Lower Permian Qixia-Maokou Formations with a measured maximum thickness up to 150m. It is proved that no one suite of carbonate source rock with a thickness over 1000m exists in Southern China. This study has bring forward some new insights into the thickness, developed zones and primary hydrocarbon-generating potential of the four suites of source rock as well as into the identification of carbonate source rocks.