In order to understand the growth characteristics of Eichhornia crassipes under shading treatments for different time and develop a new way to increase their biomass,we conducted the experiments during the summer natural condition in Nanjing in 2011.Several different time shading treatments (shading for whole day,shading during 7:00～11:00,shading during 11:00～15:00,shading during 15:00～19:00,the natural light condition as control) were set up for planting E.crassipes for 25 d.Every 5 day,the fresh weight per plant,the dry weight per plant,the photosynthesis parameters such as net photosynthetic rate (P_n),antioxidant enzymes activities and 1,5-bisphosphate ribulose carboxylase oxygenase (Rubisco) activity in leaves were measured.The results showed,as compared with CK,shading whole day decreased the leaf number and ramate number,the root length,leaf area,the fresh weight and dry weight per plant,but the treatment shading during 11:00～15:00 increased the root length and leaf area.Although the leaf number and ramet number were also inhibited at this treatment.The fresh weight and dry weight per plant were a bit increase as compared to the CK.The changes of growth were closely related to the physiological characteristics.As compared with CK,the shading treatment showed that the max net photosynthetic rate (P_nmax),superoxide dismutase (SOD),peroxidase (POD),ascorbate peroxidase (APX),glutathione reductase (GR) and total antioxidant capacity (AOC) activities of leaves during shading from 11:00 to 15:00 were higher than those of CK and exhibited a decrease of malondialdehyde (MDA) content and superoxide radical production rate,which was helpful to remove reactive oxygen species (ROS) to reduce the oxidation injury at noon;The effect on the Rubisco activity of 11:00～15:00 shading was similar to that of the CK,showed the stable activity of Rubisco.It can be seen that E.crassipes is belong to sun plants.So shading treatment whole day would inhibit the growth of the plant.While with the shading treatment at noon,it would alleviate the photooxidation damage by regulating the growth indexes and inducing the increase of the enzyme activities to keep the stable photosynthetic capability,which can increase the biomass of the plant.