The approximate expression of the steady-state response of forced power oscillation in multi-machine power system is obtained. The left and right eigenvectors and participation factors and other parameters are used to analyze the oscillation distribution characteristics of forced power oscillation in multi-machine system and the impact of the disturbance source location on the system response. The general method of power system small signal analysis is introduced based on the power system simulation software DIgSILENT. The characteristics of forced power oscillation is simulated on 4-machine 2-area power system. Then the forced power oscillation is compared with negative damping and weakly damped oscillation. It contributes to deep understanding of forced power oscillation of multi-machine power system.