In this paper, the authors considered a reservoir s pore structure to be a fractal structure. The pore-rock interface is an irregular and complex fractal surface. The pore surface has the characteristic of self-similarity, but hasn t characteristic length. The powerful tool to describe the degree of complexity of fractal pore surface quantitatively is fractal dimension, which varies from 2 to 3. The closer the fractal dimension is to 2, the smoother the surface is. The closer the fractal dimension is to 3，the more irregular and complex the surface is . This paper studied and measured the fractal characteristic of pore surface with the technique of impregnating pore space.scanning electron microscope and the method of molecular adsorption.

Analyzing and studying the fractal characteristic of pore space structure greatly contrlbutes to the evaluatlon of reservoir，the studying of residual oil （or gas）saturation and the raising of oil(or gas)recovery percent.