To improve the theoretical calculation precision of permeability coefficient for porous material, solving model of permeability coefficient was established on the basis of fractal theory, and solving method of fractal dimension was optimized by image processing. Firstly, after photographing surface image of four kinds of porous materials with a scanning electron microscope, fractal dimension was solved by box dimension method and influence of image size and amplification factor of porous material on solving precision of fractal dimension was researched. Secondly, according to Darcy law, fractal theory and corrected Hagen-Poiseulle gas equation, solving equation of permeability coefficient without correction factor was established, resulting in calculation formula of fractal theory for porous material was improved. Finally measuring platform of permeability coefficient was established, and correctness of theoretical derivation was verified on the basis of judgment result of flow state. The result indicates: with increase of image size and decrease of amplification factor, fractal dimension approaches true value increasingly; theoretical calculation value of permeability coefficient is more accurate after theoretical relation without experience parameters of maximum diameter of hole, minimum diameter of hole, tortuosity, fractal dimension and permeability coefficient is established. Error value is 5%～8% through comparing theoretical calculation value of permeability coefficient and experiment value, which can satisfy error requirement of measuring for material permeability coefficient.This paper provides new ways of obtaining material permeability coefficient accurately.