Present/absence method(observed chlorophyll-a content of nature lake phytoplankton with and without addition of Daphnia)wereused to estimate grazing capacity of Daphnia longispina grazing on phytoplankton in Lake Taihu in April, 2006. The results showed thatthe ingesting rate was 0.0011-0.0245μg/(ind·h). There was very nice regression connection between density of D. longispina andingesting rate(R²=0.8836). It was parabola which had maximum value. The ingesting rate of D. longispina and food concentration had alinearity connection(R²=0.8586). The ingesting rate of D. longispina in the present experiments was higher in the dark groups than that ofthe light groups(P<0.05, test).D. longispina grazed most effectively on phytoplankton such as Scenedesmus and Cyclotella, the selectivefeeding indices were 0.5425 and 0.5079. However, D. longispina did not like to eat Ulothrix, the selective feeding index was -0.7039.