Determination of minimum discharge is the focus of the environmental impact assessment. In the case of Jinsha Hydro - electric Power Station, based on the comprehensive evaluation of the hydraulic shape elements and Hydraulics factors such as water depth, flow velocity, flow width, wetted perimeter frequency and flow area, this paper determined the minimum discharge at the Jinsha Hydroelectric Power Station by using eco-hydraulics method to meet the necessary conditions of fish breeding production in downstream river.