The full field observation of infrared thermography（IFG） is used to determine resonant frequencies of a PZT—5 piezoceramic rectangular plate specimen and to observe the stress distribution in the specimen with the purpose to verify the applicability of IFG in vibration mode investigation of piezoceramics.The eight resonant frequencies of the specimen obtained by IFG agree well with those obtained by transmission line method（TLM）.The thermographs of the specimen vibrating resonantly are basically in accordance with the ANSYS modeled pictures of stress distribution of the specimen.It is concluded that infrared thermography can be used as a major method for study on vibration modes of the piezoceramics.And it is guidable for designing and appling piezoceramic transducers.