Based on flow experiments of reservoir sensitivity, combining with X ray diffraction, scanning electron microscopy, casting thin and so on, clay mineral characteristics and its effect on sensitivity of Fuyu ultra low permeability reservoirs in northern of Fuxin uplift are studied. The results show that Fuyu reservoir contains mostly chlorite, illite, kaolinite and illite/smectite mixed layer, illite is much more than chlorite and illite/smectite mixed layer, kaolinite is at least. Speed sensitive and alkali sensitivity are relatively weak, water sensitivity and salt sensitivity are strong and have a great impact on the reservoir, exploration and development should focus on them. Clay mineral has mainly three effects on reservoir water sensitivity, clay mineral total content has a main control on water sensitivity.