The space-time distribution features of frequency responses were proposed to analyze varieties between the disturbing source generator and generators in the same/different areas in power system forced oscillations．The oscillating components of various frequency increments had different initial phases which resulted in different time of the first oscillating extreme value for the frequency increments in forced oscillation．The frequency increments of the disturbing source generator always achieved its first oscillating extreme value earlier than which of other generators．The delays of other generators in the same area with the disturbing source generator were determined by the value and initial phase of intra-area oscillating frequency, meanwhile, the delays of other generators in another area with the disturbing source generator were determined by the value and initial phase of inter-area oscillating frequency．Both the theoretical and practical case study showed that utilizing space-time distribution features of variational frequency responses could analyze forced oscillation effectively and locate disturbing source generator.
