Abstract: Three typical arid clumpassembled communities (grassforb, shrubgrass and arborgrass in lifeform composition) were selected at Xidatan, Pingluo County, Ningxia Hui Autonomous Region to study the special distribution patterns of root systems and soil water contents, as well as the relationship between soil site conditions and vegetation types. Accordingly, three subareas (namely undercanopy, transitional and openland) were partitioned out in each community to represent the different microhabitats from the base of clumps to interclumps bare land. For each subarea in the three communities, soil bulk densities, root biomass densities, soil water contents in the 5 sequential soil layers (0-10 cm, 10-30 cm, 30-60 cm, 60-100 cm and 100-150 cm in depth) and soil surface steady infiltration rates were measured respectively. The results showed that: (1)Surface steady infiltration rates increased from openland to undercanopy subarea in each community, indicating that the growth of plants can significantly improve the soil infiltration rate; (2)Steady infiltration rates in openland subarea where affected little by plants and represented relative original site condition were higher in arborgrass community than in shrubgrass community to some extent; (3)In each community, the highest fine root biomass density in undercanopy subarea was in 0-10 cm soil layer, but in deeper layers in transitional and openland subareas; (4)Inversed soil water content gradients were detected in the three communities during the sampling period, especially in the undercanopy subareas. And the trends behaved the most intensively in the grassforb community, but the least in the arborgrass community.