In determining the noise and vibration control of a machine structure，it is important to clarify the exciting sources and vibration transmission paths. However，the noise sources do not always coincide with the origin excited in a structure. It is necessary to identify the excitlng sources and vibration transmission paths on the plate and beam. To satisfy this requirement，vibration intensity measurement has been used. This paper describes the detection of vibration intensity vector in flat plates using three-channel method. In this method，the amplitude and direction of vibration intensity vector are obtained by processing three output signals from accelerometers set on plates. Using this method vibration intensity vectors around the exciting point on a steel plate are measured. The measuring errors in amplitude and direction are discussed. The detection limits on vibration frequency，stiffness of plate and weight of the probe are investigated. The vibration power of bending wave was calculated by integrating the vibration intensity vectors and compared with exciting power measured by an impedance head．The result shows that three-channel method can be used to detect the vibration intensity vectors in flat plates. This method was applied to identify the source of excitation in gas heat pump package panels.