Abstract: The effects of different water level gradients on the stem length, number of clonal ramets, biomass accumulation and biomass allocation patterns of 3 aquatic plants, namely Pontederia cordata, Acorus calamus, and Iris wilsonii were studied through artificial simulation of water level control experiment. Two sets of treatments were designed with water levels for the fixed water levels (including low water level that submerged 1/2 of the pot height, medium water level that reached to the right top of pots and high water level which exceeded the pot top by 12cm) and the fluctuated water level (i.e. low water level to 1/2 of the pot height for 14 d, then transferred to high water level that exceeded the pot top by 12cm for 7d), and the 2 water levels alternated in turn for 56d, and the entire test duration was 8 weeks. The results showed that the water level gradients significantly affected on the above indexes observed of all the 3 species. The indexes of plant height, number of ramets of Pontederia cordata, Acorus calamus plants treated with the fluctuated water level were all significantly higher than those plants treated by the fixed water level (P<005). The biomasses of the rhizomes, leaves and root system of Pontederia cordata plants treated with the fixed high water level as well as with the fluctuated water level were all significantly higher than those plants treated by the fixed medium and low water level. Only the leaf biomass of Acorus calamus was significantly affected by the fluctuated and the fixed high water levels treatments, whose value was significantly higher than that of treated by the fixed medium and low water level. There was no significant difference in the biomasses of leaves, rhizomes and roots of Iris wilsonii among the different water level treatments (P>005). Comprehensive speaking, the fluctuated water level treatment was more beneficial to the population establishment of the three aquatic plant species.