Abstract: The anatomical structure of the secondary xylem of Quercus mongolica tree species was observed and analyzed by means of applying timber image analysis system and photomicrography observation method. The observation showed that the secondary xylem of Q. mongolica was composed of duct, ring tube tracheid wood fiber, wood ray and axial parenchyma cells. In the ontogenetic process of Q. mongolica,the size of tubular molecules of roots and branches was significantly smaller than that of the trunk, and there were significant differences in the morphology and distribution of these molecules.The segregation of secondary xylem showed that Q. mongolica was single perforation, pitting tube between each row, majority of the ducts were in the form with a tail at both ends, and the length of the ducts was greater than the width. This phenomenon showed that the evolutionary process of Q. mongolica was not synchronized.