That the grain sizes are between 0.2～50 μm have fractal property.Acoording to the principle of the fractal geometry

the expressions of pore size distribution curve

capillary pressure curve

J function curve

relative permeability curve and equilibrium contact angle of the reservoir rocks could be derived.Leverett.et.al show that the reservoir rocks with the similar properties have unique J fanction curve.The expression derived for J function curve indicates that the reservoir rocks of this kind have the similar fractal dimension and pore tortuosity.The expression of the capillary pressure and J function curve could be used to calculate the fractal dimension of the reservoir rock pore structure and its change after the water sensitivity or acidizing.This method is simpler than scanning electron microscopy.