Poyang Lake is a water-passing and river-injecting lake with an unique river-lake two-phase nature.The lake current and the water quality is quite different between river shape and lake shape.Based on the simultaneous monitoring data of lake current and water quality from 2010 to 2016，mathematical statistics method is applied to study the variation characteristics of lake current and water quality under the different cases of river shape and lake shape of Poyang Lake.The results show that：1)The velocity of the lake area in the northern part is greater than that in the southern part than in the eastern part of Poyang Lake.The velocity in the main channel is greater than that in the continental sand beach；2)The average velocity of the lake phase are lower than that of the river phase.The flow velocity increases from the increase in the water level under the river phase，decreases from the increase in the water level under the lake phase；3)The TN and TP values of the river phase are larger than that of the lake phase.The eutrophication index of the river phase is lower than that of the lake phase；4)TN and TP generally appear and transfer in the form of clusters or patches，and the degree of overlap of the over-standard water areas between them are smaller in the lake area.