Based on the series hydrological data of the head of Waizhou hydrological station in the lower reaches of Ganjiang River，this paper analyzes the inflow situation of Nanchang reach of Ganjiang river and the basic conditions for guaranteeing the water source and water quantity of the urban residents in Nanchang city，which indicates that the surface water of Nanchang reach of Ganjiang river can basically meet the ecological water demand of the river on the premise of guaranteeing the water use of the urban residents in Nanchang city；and according to the water resources bulletin of Nanchang the monthly report analyses the water quality and water quality guarantee of Nanchang reach of Ganjiang river，which shows that the water quality guarantee of urban residents in Nanchang is good.