With the completion and operation of several world-class high dam reservoirs in the Jinshajiang River watershed, the high sensitivity and vulnerability of the reservoir water level fluctuating zone (WLFZ) ecosystem have become increasingly prominent. How to restore the vegetation in the WLFZ is of great significance to protect the stability and diversity of ecological functions and maintain a critical cycle of the ecosystem. With ecological niche theory and interspecific relationship analysis methods, including ecological niche determination, variance ratio method, χ² test, association coefficient A_C, Ochiai index O_I, Pearson correlation coefficients and Spearman rank correlation coefficients, intrinsic interspecific linkage, ecological adaptability and community succession status of dominant plants in the WLFZ of the Jinshajiang River Reservoir were revealed. The dominant plants were classified into three ecological species groups to provide reference for suitable plants and their scientific allocation for ecological restoration in the WLFZ. The results show that: 1) A total of 37 plant species belonging to 19 families and 36 genera were recorded in the reservoir WLFZ of the Jinshajiang River watershed, and the dominant species at a frequency of ≥20% being Cynodon dactylon, Polygonum lapathifolium, Symphyotrichum subulatum, Eleusine indica, Alternanthera sessilis, Abutilon theophrasti, Chenopodium ambrosioides and Xanthium sibiricum, in which C. dactylon had the greatest importance value and ecological niche width, dominating the absolute competition. 2) The overall similarity and overlapping in ecological niches of dominant plants in the WLFZ are small, and the similarity in resource use is low, indicating high degree of ecological niche differentiation between dominant plant species. 3) The overall connectivity of dominant plants shows non-significant negative associations, and the overall stability of the community is poor. The χ² test, Pearson correlation coefficients and Spearman rank correlation coefficients all showed low significance and weak interspecific linkages. Based on the results of the ecological niche and interspecific relationship studies, eight dominant plant species are recommended as pioneer species, and the three ecological species groups are allocated along the water level gradient according to the delineation, so that the interspecific plant relationships evolve towards harmony and benefit the natural restoration process of the vegetation in the WLFZ.