A new method of identifying the power system oscillation property using decomposition of energy supply on the port（ESP）is proposed.Component decomposition of ESP is conducted and found to show that the trend component of ESP changes exponentially under weak damp oscillation while linearly under forced oscillation，respectively.ESP is calculated using the component of dominant mode in electrical variables，which are acquired by empirical mode decomposition（EMD）.The trend components of ESPs are also obtained by EMD with the obvious trend component of ESPs fitted by exponential and linear curves，respectively.The correlation coefficients between real trend component and fitting trend component are calculated under two fitting types.The change rule of the trend component is determined by fitting error indices and the correlation coefficient.The oscillation type is identified according to the identified change rule.Finally，the simulation analysis of an IEEE 39-bus system and the instance analysis of a real power plant has proved the validity of the proposed method.