针对飞仙关水电站下游峡口“阻流顶水”现象，为拓宽峡口过水面积，降低坝下水位、减小汛期防洪压力、增加发电效益，开展了电站下游峡口拓宽优化设计；经峡口拓宽开挖方案设计，拓宽前后水位流量关系曲线对比分析、动能分析论证后，通过装机容量微调、机电及厂房结构、金属结构设计部分调整，达到挖潜增效的目的。最终设计优化方案较原设计电站单独运行及联合运行的年发电量、枯期发电量都有明显增加，补充单位千瓦投资和补充单位电能投资均较低，经济效益明显。

The choked flow and top water exist in the Feixianguan Hydropower station. For the sake of widening the discharge area of narrows, lowering the water level of the downstream, reducing the pressure of flood control during flood season as well as increasing benefit of power generation, the optimization design of widening the downstream narrows of the hydropower station is performed. It is verified by widening excavation plan and contrast analysis of stage-discharge relation curve and kinetic energy before and after widening that economic benefit can be improved by means of adjusting installed capacity, electromechanical system, power house and metal structure. Finally, comparing with the old design, the generated energy of each year and during arid period under independent and combined operation of hydropower station both increase obviously after optimization design. Meanwhile, the supplementary investment of per kilowatt and electric energy are relatively low which bring about significant economic benefits.