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The objective of this study was to clarify the characteristics of fine roots (diameter d ≤2 mm) parameters (root biomass, root length density and specific root length) in 0~20 cm soil layer under different plant communities in forest zone, forest steppe zone and steppe zone of the Yan river basin in hill-gully region of Loess Plateau. Soil drill method was used to collect root samples. Vernier caliper was used to measure root diameter in two grades of 0~1 mm and 1~2 mm. Root length of two diameter grades was measured, then root samples were dried to constant weight at 85℃ and weighed. The main results were as follows: (1) In the three vegetation zones, the proportion of root length density ( d ≤ 1 mm) and root biomass of different communities accounted for 90% and 53% of the total fine root, respectively. The root ( d ≤1 mm), which accounted for a large proportion of the total fine root, not only contributed greatly for the plant growth, but also played an important role in improving soil structure. (2) Root biomass ( d ≤2 mm) of different plant communities showed a decreasing trend from southern forest zone to northern steppe zone, while specific root length showed a increasing trend from southern forest zone to northern steppe zone, root length density in steppe zone was significantly lower than those in other two vegetation zones ( P < 0.05). The variation tendency of root length density and root biomass was the same, and root length density and root biomass of tree community and shrub community were higher than those of herb community. But specific root length of herb community was significantly higher than those of tree community and shrub community ( P <0.05). (3) Root length density and root biomass of tree community, shrub community and Lespedeza davurica dominated community were higher than those of other communities, the root growth of these communities was vigorous, and root system of these communities developed well. The specific root lengths of Sophora viciifolia , Periploca sepium and Bothriochloa ischaemun respectively dominated communities were higher than those of other communities, thus these communities had stronger potential ability to absorb soil moisture and nutrients, and higher growth rate. (4) The root parameters of Sophora viciifolia, Periploca sepium, Artemisia gmelinii and Bothriochloa ischaemun respectively dominated communities, which distributed in forest steppe zone, were significantly bigger than those of other communities distributed in the other two vegetation zones ( P < 0.05). It indicated that these communities could absorb soil moisture and nutrients more efficiently and play an important role in increasing soil anti-erodibility in forest steppe zone.