Through the introduction of development on dew point indirect evaporative cooling technology at home and abroad,the author put forward an air conditioning unit based on dew point plate indirect evaporative cooler,which is called dew point indirect with direct evaporative cooling air conditioning unit.And analyzed the principle and characteristics on it.The result shows that it can achive more higher temperature drop than the traditional dew point indirect evaporative cooler,thus it become much closer to the dew point temperature of outdoor air.It′s a new development of dew point indirect evaporative cooling technique.Meanwhile it proposed some research methods on performance testing of the unit.