The geochemical characteristics of the 4 sets of regional high-over mature marine source rocks are as follows: (1) The kerogen maceral is mainly Type Ⅱ, also there are some Types I and Ⅲand the δ13C of kerogen and the extracted bitumen "A" get heavier as the geological time gets younger, which reflects the increasing of the higher plant inputting. (2) The content values of extracted bitumen "A" and total hydrocarbon in Upper Paleozoic source rocks is 6~10 times of those in the over mature Lower Paleozoic source rocks. Compared with the low mature source rocks in the identical strata, a large amount of hydrocarbon has already been expulsed out from the high-over mature source rocks. (3)The bimodal n-alkane distribution of the extract from the Lower Paleozoic source rocks represents the input of two different kinds of aliphatic chain algae, and the existence of both bimodal and unimodal distributions of the extract from the Upper Paleozoic source rocks reflects the different contributions of aquatic organism and higher plant. (4) The Pr/Ph ratios and the routine biomarkers of steroid and terpane are so convergent in distribution as to lose effectiveness, which results in difficulty to differentiate from the source rocks in the different formations that are used to oil-source correlation. (5)The special biomarkers, such as triaromatic steroid and methyl triaromatic steroid, and especially triaromatic dinoflagellate sterane, can be used to distinguish the source rocks in different regions and different formations so that they can be used to oil-source correlation. The distribution of these compounds is reduced from Cambrian to Permian and the concentrating areas of these compounds basically accord with the generating centers of the different formations, so they can be used to locate the positions of hydrocarbon source areas.