Abstract: Distinguishing hydro-unit vibration zones is the core that affects safe and economical operation of a hydropower plant. This study focuses on the difference in hydro-unit vibration intensity under different loads and adopts an idea of graded vibration zones, i.e. dividing the vibration zone into an operation-forbidden zone, an unrecommended zone, and a stable zone. Then, we construct an in-plant economical operation model of hydropower stations taking these graded zones into account, and solve it using a particle swarm algorithm. Application to the Zangmu hydropower station shows that in comparison to a single operation-forbidden zone, this new method predicts an increase as low as 0.69% in the water consumption by the plant operated in the allocated output mode, while keeping unit operation more stable with lower vibration. Thus, adoption of graded vibration zones improves model applicability to the real conditions of a hydropower station and helps find operation schemes that are more economical.