Abstract: Chang 3 member is the main oil producing layerin Yanchang formation of Xunyi Block.On the basis of the previous research,this paper analyzes the development characteristics of the surplus pressure and the relationship between surplus pressure and hydrocarbon accumulationusing the principles of reservoir forming dynamics and pressure seal box, combined with the core test and the analysis data.The results show that:vertically, the pressure structure decides the development horizon of the reservoir, i.e. Chang 7 reservoir accumulates oil and gas in the pressure storage tank under a sudden pressure structure; Chang 3 and Chang 6 reservoir accumulates in the upper gradual change zone under a gradual changing pressure structure.Horizontally,the surplus pressure controls the plane distribution of oil and gas reservoirs.Both Chang 6 and Chang 7 reservoirs are located in the area with high residual pressure and sufficient charging power, which is conducive to hydrocarbon accumulation. The research is of guiding significance for the future exploration and deployment of tight oil in Yanchang formation of Xunyi block.