Abstract: Vegetation of the Oryza rufipogon Reserve, in Chaling, Hunan Province was surveyed with 2 m ~ 2 m quadrats and a community horizontal structure map drawn. In total, ninety random sampling quadrats in nine plots under different ecological conditions were surveyed. Several basic descriptive statistical indices were chosen to characterize patch size and spatial distributions. The niche breadth and niche overlap of the ten dominant species were measured on indirect habitat gradients and niche ordination was calculated from the overlap matrix. The results showed that the species distribution was heterogeneous and that niche separation was found among the ten species. The ecological distributions of these species were determined by heterogeneous environmental factors, especially hydrological factors. Ten species occupied a continuum along a water availability gradient, which was divided into 3 groups based on niche ordination: Brasenia schreberi, Murdannia triquetra, Nelumbo nucifera, Eleocharis acutangula, Scirpus triangulatus, and Sagittaria trifolia were found in water deeper than 20 cm. O. rufipogon and Leersia hexandra occurred at a depth of 10 cm to 20 cm. Isachne globosa was found at a depth of less than 10 cm. The maintenance of the suitable habitat, especially the suitable water level, is essential for the conservation of O. rufipogon.