Abstract: How to locate the disturbance source in forced power oscillation is an important issue in the diagnosis and analysis of lowfrequency oscillation. Definite attention has been drawn on the identifying of disturbance source with the data provided by phasor measurement unit（ PMU）. Currently, however, the limited number of PMUs equipped in power systems is generally not considered in existing researches in this area, which makes the proposed method difficult to apply in actual power systems. For this reason, an approach to locating the source of forced power disturbance considering the unobservability of PMU information is proposed. And the basic requirements for PMU partition configuration from the angle of locating the disturbance source are presented. Simulation results show that the proposed method is capable of achieving accurate location identification of the disturbance source considering the unobservability of PMU information.