Abstract: In order to research root cortical thickness and anatomical structure of root, the high starch cassava cultivar‘Xinxuan 048’,‘Fuxuan 01’and low starch cassava cultivar‘SC124’were studied. The study determined the starch granule size which included in root’s cortex and starch storage area, root’s cortical thickness and a number of physiological indexes about root’s cortex and starch storage area. By comparing three cassava cultivars, there were four discoveries. Firstly, starch grain in the starch storage area was longer than that in the cortex. Secondly, starch grain in the two plant tissues of the low starch cultivars‘SC124’was shorter than that of the other two high starch cultivars. Thirdly, cassava cortex thickness was negatively related with the accumulation of starch content, which was especially obvious between the cassava cultivars of genetic relationship. Finally, from the physiological index determination of the root cortex and the starch storage area, it was discovered that 3 kinds of soluble sugar and soluble sugar accumulation in the cortex was far greater than that in starch storage area, and the difference was the most significant in high starch cultivars, it showed that the root cortex plays a key role in starch accumulation.