The upper reaches of the Minjiang river is the transition zone from the Qinghai-Tibet Plateau to the Sichuan basin. It has a typical arid valley climate with complex topography and variable water and heat conditions. A long history of anthropogenic impact in combination with a severe natural environment has resulted in degraded vegetation dominated by xeric shrubs. Therefore， it is important to understand the process of ecosystem dynamics. Biocomplexity theory is becoming increasingly important in understanding natural vegetation dynamics. In this study, based on the field investigation of plant species and environmental factors (slope, elevation, aspect, soil water content and soil nutrients) in the arid valley of Minjiang River, we studied plant community complexity, and its relationship with environmental factors, community diversity, species evenness and richness. Six transects were set up along the arid valley of Minjiang River. Both total and structural complexity of communities showed a "high-low-high" tendency with the increase of elevation in the study area, which meant that the complexity of communities was highest at the sites of low and high elevation, while the lowest was at the sites of middle elevation. The transects at the center of the valley had lower total complexity than those at the north and south sides of the valley, which probably due to the differences of environmental conditions. We found that both total and structural community complexity varied with degree, shape and aspect of slope, with an order of upper slope>middle slope>lower slope, shaded slope> half-shaded slope>sunny slope, and concave slope>straight slope>convex slope. Our study indicated that Form. Pertyasinensis,Jasminumhumile had the highest total complexity, and Form Leptodermispurdomi and Form Ceratoidesarborescens communities had the lowest total complexity, while Form Quercuscocciferoides and Form Onosma farrerii communities had the highest structural complexity. We also found that total community complexity had significant quadratic correlations with soil organic matter (SOM) content, total nitrogen (N), hydrolyzable N, soil water content, and available potassium (K), respectively, while it had no significant correlations with soil total K, total phosphorus (P), available P, and pH value. Total community complexity positively correlated with community diversity, evenness and species richness, while structural complexity negatively correlated with community evenness. As two components of total community complexity, structural complexity was more sensitive than diversity to the change of species in the community, which was not only related to community evenness, but also to community richness. The relative contribution of structural complexity and diversity to total complexity would be different for different study area or ecosystems.