With the petroleum-contaminated soil under Ricinus communis L. phytoremediation in Shenfu irrigation area of Shenyang as test material, this paper studied the quantitative variations of bacteria and fungi, physiological and biochemical characteristics of dominant microbial species, and nutritional types of bacteria in root zone, rhizosphere, root plane and root inside. The results showed that the quantity of bacteria decreased in the order of rhizosphere > root plane > root inside, while that of fungi was in the sequence of root inside > root plane > rhizosphere. The dominant species of bacteria and fungi were most abundant in root plane and root inside, respectively, and the dominant bacterial species in root plane and root inside had a stronger capability in degrading macro-molecular substances. The nutritional demand of bacteria in root plane was of amino acid type.