Abstract: A comprehensive data-model-driven analysis method is proposed to address power oscillation issues in hydropower stations with expanded unit connections. First, the damping performance of the Power System Stabilizer (PSS) under active power step disturbances is calibrated. After confirming that its damping performance meets the specification requirements, 50% and 100% rated active power load rejection tests are conducted to reproduce the power oscillation phenomenon. Oscillographic recording data are analyzed to rule out hydraulic system disturbances and generator out-of-step faults. The test results show that the PSS provides inadequate damping against large disturbances. Subsequently, a disturbed system model is established to investigate the physical mechanism of generator oscillation. Two control strategies are formulated to improve unit stability: limiting the leading-phase operation depth of generating units and implementing rapid load shedding upon oscillation occurrence. Field test results finally verify that the proposed strategies possess remarkable oscillation suppression capability. This research can supply quantitative references for power oscillation analysis and decision-making in practical hydropower stations..