Abstract: With mesocosm experiment effects of different light intensity on morphology and structure of Potamogeton crispus were studied.The results showed that the mean difference in the total biomass of P.crispus under the condition of 100% and 50% of natural light intensity(NLI) was not significant.The total biomass of P.crispus was markedly decreased with the treatment of 20% and 10% NLI.In biomass distribution,rates of root/shoot with treatment of 50% NLI were much higher than other treatments,which indicated more biomass was distributed to above-ground shoot.Height of shoot,number of leaf and number of leaf in canopy of P.crispus with the treatment of 50% NLI were much more than other treatments,which showed the treatment of 50% NLI facilitated growth of this species,but the treatment of 10% NLI restrained growth of P.crispus.The thickness of leaf in P.crispus increased under the condition of the treatment of 20% and 10% NLI.The thickness of leaf with the treatment of 100%,50%,20% and 10% NLI were 0.260 mm,0.297 mm,0.440 mm and 0.306 mm,respectively.With the treatment of lower light intensity,mesophyll cells became bigger,and mesophyll cells shaped bigger ventilating tissue.Cell area of ventilating tissue with the treatments of 100%,50%,20% and 10%NLI were 0.108 mm²,0.087 mm²,0.558 mm² and 0.284 mm²,respectively,which showed that the treatments of 20% and 10% NLI were much more than those of 100% and 50% NLI.Crystals were observed in epidermis cells of root with the treatment of 20% NLI.The bigger ventilating structure was observed in cortex of root with the treatment of 50% NLI,but this structure did not existed in other treatments.The results indicated the treatment of 50% NLI was in favor of growth of P.crispus.