Abstract: Geologic Bodies have complex self-similar construction，and therefore are suitable to be described by fractional demension. Taking as an example the porosity data of reservoir Ma 5. 1 in the middle gas pools in Shan-Gan-Ning Basin，this paper studies the application of the fractional theory in studying non-homogeneity of reservoirs，the result of which is satisfactory.

Key words: Reservoir Characteri3tics, Porosity distribution, Fractional dimension, Non一homogeneity, Mathematical geology