The Chang-8 Unit of the Yanchang Formation is a major reservoir in Jiyuan area, Ordos Basin. However, the reservoir shows strong heterogeneity and oil production varies from well to well dramatically. In this paper, samples from 4 drilling wells were selected to conduct relative permeability sensitivity test so that the percolation characteristics and their influence factors can be studied during the reservoir water-flooding process. The purpose of the research is to analyze micro-pore structures of the reservoir, clay minerals, and the impact of diagenesis on relative permeability curve.