Abstract: Tree root system is one of the most complex parts of the underground ecosystem. The accuracy and comparability in root ecological function studies is limited by highly heterogeneous morphology and structure. The reasonability of definition on fine roots of Metasequoia glyptostroboides was discussed which could improve fine root studies in the future. We determined fine root anatomical structures and root mycorrhizal colonization with different orders in M. glyptostroboides plantation and explored the relationship between fine root morphology and anatomy. We found: firstly, it was more reasonable to classify the roots by root order, and 1,2 level roots were defined as fine roots; secondly,1,2 level roots were those ones with intact epidermis, thicker and multi-layered cortex, and 3, 4 level roots were skinless roots or only a small amount of residual epidermal cells, with root orders increased, roots cortex layers and epidermis thickness became significantly lower; thirdly, with the root order increasing, the degree of cork periderm was significantly increased, vascular tissue development was gradually improved, the diameter of the vascular tissue and the ratio of vascular tissue to root diameter(V/R)was increasing with root order increase. There were significant correlation(except root level)between fine root diameter and vascular tissue diameter, but there was no correlation between fine root diameter and the cortical parenchyma cells diameter or cortical layers; fourthly,the mycorrhizal colonization in 1-3 order roots could be observed, and with root order increase, the mycorrhizal colonization rate was significantly decreased. There were obvious differences in fungal infestation area of single individual root with different order. In the future study, we should combine fine root morphology investigation and anatomy characteristics to investigate the correspondence between the root order and root diameter, and then determine the division of the range of fine roots.