Abstract: It has been confirmed from exploration that Yuanba area in northeastern Sichuan basin is rich in oil?gas resources in its marine carbonate reservoir. But at present, fewer researches focus on its cap rock studies. This paper analyzes the typical well logging response of the gypsum?salt cap rock, and by fine interpretation of this rock, presents their statistical thicknesses in different horizons. The results show that the gypsum?salt zones are vertically distributed in Leikoupo formation, Jialingjiang formation and the fourth member of Feixianguan formation, of which Jia No.4?Jia No.5 and Jia No.2 members as two sets of gypsum?salt rocks are of the largest single thickness and cumulative thickness. In plane, these two sets of gypsum?salt rocks are characterized by thinning to the west and north and thickening to the east and the south, as well as good continuity and big thickness, which should be the high?quality cap rocks in this region