Traditional reservoir operation is mainly designed for water supply and/or flood control, ignoring ecological demand of the river. so that the natural hydrological process in the river has been changed, the ecosystem has been threatened, which will impact the maintainable use of the water resource. So it is necessary to adjust and optimize the traditional operation. Using RVA method, this paper analyzes the ecological water demand of the Nenjiang River and the influence to ecological flow in the river caused by the current operation of Nierj Reservoir, the ecological reservoir reoperation model is also established. then suggestions on optimizing the current operation of the reservoir are elaborated.