Water quality and distribution of Vallisneria natans in the Litang River in Shanghai were investigated in 2012. We also studied the effects of different light intensity on the growth and photosynthetic oxygen evolution rate of V.natans. Results showed that the transparency of Litang River was 80-100 cm,and when the water depth increases, the V.natans biomass firstly increased and then decreased,and the turning point is at the depth of 60-90 cm in the four experiment groups,which showed the largest biomass.The density of V.natans was negatively correlated with the depth of water while the average leaf length of V.natans was positively correlated. Investigation showed that plenty of V.natans was found in offshore area of the river, but no V.natans was found in the center of the river. Experiment in lab circumstances showed that plant biomass, tiller number,average root length and photosynthetic oxygen evolution rate of V.natans were all reduced with the decrease of the light intensity (P<0.01). The critical light intensity of V.natans was 10 μmol/(m²·s),and at that point, the photosynthetic oxygen evolution rate was 10.52 μmol/(g·h),and the V.natans biomass started to decrease. This study showed that the V.natans distribution at different depth in Litang River was consistent with transparency. This study further revealed the reason why V.natans communities were difficult to reproduce and spread in low light conditions.