Based on the two low-frequency power oscillation events in a regional grid， the mechanism of power oscillations are described in detail. Corresponding solution methodologies are proposed accordingly. The characteristics of the oscillations are obtained and analysed through phasor measurement unit（PMU） measurements. Theoretical calculation is conducted using single machine infinite bus system model. Time domain simulations using BPA software is also performed following the scenarios of the two events. Consequently， the two events have been proven to be forced low frequency oscillations. Furthermore， based on discharge characteristics of the two events together with field test， it has been identified that the source of disturbance is wobbling of the controlvalve. Finally， discharge characteristic at the inflection point is meliorated through optimizing discharge characteristics of the governing valve， as such further forced low-frequency oscillation events can be avoided.