This paper studies the characteristics of the petroleum migration and accumulation in the Yanchang Formation by means of nitrogen compounds analysis of crude oil, organic inclusion analysis, fluorescent thin slice analysis of oil-bearing sandstone, in combination with physical properties of crude oil, the correlation between oil-bearing characters and physical property changes of sandstones, and so on. Late Jurassic – Early Cretaceous is the main accumulation period of petroleum in the Yanchang Formation. At present, petroleum accumulation remains being injected into reservoirs under abnormal pressure, and repeated high-pressure charges make reservoirs located in the passage of cracks connecting oil sources be infilled again and again, so that valid accumulations of petroleum are generated.