Nitrogen (N) and phosphorus (P) availability limit plant growth in most terrestrial ecosystems. Plastic responses of plants to N and P supply cause variation in biomass and N/P ratios, associated with differences in root allocation, nutrient uptake, biomass turnover and reproductive output. We investigated the growth characteristics and nutrients acquirement of four dominant herb plant species (Bidens pilosa, Xanthium sibiricum, Polygonum hydropiper, and Chenopodium album) sampled from Zigui water-fluctuation-zone of Three Gorges Reservoir by pots cultivation at three N and P levels. In the process of plant growth, we determined plant biomass and nutrient contents of plant tissues. N contents of plant growing in soil ranged in 7.98-19.4 mg/g, and P, ranged in 0.740-3.880 mg/g, and N/P, ranged in 3.48-13.70, which indicated that plants were under N limitation. After N & P supply, N and P contents increased significantly, and plant growth were not limited by N. By comparing the growth characteristics of 4 plant species in soil, the following results were obtained. B. pilosa had significant higher biomass, relative growth rate and root/shoot biomass ratio. After N & P supply, B. pilosa growth were promoted significantly. B. pilosa would be dominant community in soil of poor nutrient level in water-fluctuation-zone of Three Gorges Reservoir.