With the deepening of oil and gas exploration, new discoveries have been made in ultra-low permeability tight reservoirs of Chang 8 reservoir in the lower Yanchang formation, Ordos Basin in recent years. However, there are distinct differences in oil charging among wells and the reservoir characteristics and main controlling factors need to be further clarified. Through new drilling, mud logging, fluid experimental and lab test data, as well as geochemistry and wireline logging analysis, comprehensive study were carried out to reveal the main controlling factors of hydrocarbon migration and accumulation and differential distribution law in Chang 8 reservoir on the basis of exploration data as well as previous research results in southwestern margin and adjacent region of Ordos Basin. The results show that contrast to inner basin, the fluid properties is worse, hydrocarbon charging scale and degree is smaller in southwestern margin. The major formation reasons of enrichment difference are source rocks quality and reservoir forming power. The sand body and reservoir physical properties is not so important. Structural adjustment influence secondary oil-gas migration or damage in southwestern margin contrast to basin center, resulting in lower enrichment degree of marginal reservoir. Unlike the high quality source, high pressure and strong charging mode in the basin center, the oil and gas at the edge of the basin should adopt a low generation, low pressure, and low charging reservoir formation mode. In order to achieve best selection and optimization in the poor edge area, more attention should be paid to the fine evaluation of the source rocks and the analysis of preservation conditions.Through the above research, comparative study should strengthen more in order to further understand the distribution law of low permeability to tight oil and provide effective guidance for tight oil exploration of complex marginal area.