Oil and gas exploration has achived appreciable progress in Nanpu sag with the highest oil and gas accumulation degree of Bohai Bay Basin, China. The oil and gas reserves has been much higher than the oil and gas resources evaluated before. It was thought that the total organic content(TOC) of source rocks in Nanpu sag is low, with the number of 0.8%-1.2%, which resulted in the low hydrocarbon resources. This research shows that high quality source rocks which is comparable with that of Shahejie Formation in Dongying sag [1, 2] exist in Nanpu sag and the hydrocarbon accumulation conditions are excellent. Organic matter-rich source rocks are identified within Shahejie Formation(Es), especially in Es34 member with the TOC up to 5%. It’s a suit of mature source rocks with the TOC generally more than 2%, S1+S2 more than 20mg/g, Tmax above 440℃. Laminas of organic matter-rich shale are developed, mainly including organic laminas and calcareous laminas, with kerogen and mineral interbeded. It’s easy to identify shale from surrounding rock according to obvious reflection enents and logging response of petrophysics. Laminated texture comporised of organic-rich clay layer and fine-calcareous laminas is the remarkable characteristics of Es34 formation. The horizontal clay layer, containing clay minerals and pyrite et al., is the deposition in standing water. The thickness of effective source rocks within Es34 formation is about 250m, and high quality source rocks around 100m. Ro is more than 0.8% and the organic matters are mainly from amorhpous mass and phycoplast. Source rocks within Es34 formation were formed in the early Eocene period when major faulted depression movement occurred. The lake basin occupied the largest area and water depth reached the highest level in history [3]; Widespread gray or black mudstone, calcareous mudstone and oil shales in thickness prevailed over the stage, which had great potential of hydrocarbon generation. Source rocks in Es33 formation is also of high quality, second only to that within Es34 formation. On the whole, source rocks in Es3 formation is the best, Es1 formation is next. At present, source rocks within Es34 formation have past its generation peak according to the burial depth of 5800m~6400m. Accumulation conditions in Nanpu sag is quite good. First, the Tertiary source rocks within Guantao formation had began to generate a large amount of hydrocarbon before the volcanic eruption which formed many hydrocarbon migration pathways like faults and contributed to hydrocarbon migration and filling. In addition, hydrocarbon enrichment factors are also based on kinds of migration pathways, multiple hydrocarbon source beds, multiple injection, compact balsalt cap rock and time-space matching(Fig. 1), especially the following two factors. (1) Igneous cap rock. Widespread basalt cap rock with large thickness is developed in Nanpu sag, with the thickness up to 500m, much of the region 50m, which other fault basins do not have. (2) Fault-based hydrocarbon migration pathways. Faults are the most important hydrocarbon migration pathways for every oil-bearing series in Nanpu sag, as well as the most important conditions for the multiple hydrocarbon accumulation. Many faults connected to source rocks or the basement rock are good migration pathways, so that sand bodies connected with the fault are full of hydrocarbons and there are many production layers in vertical.