Abstract: The real atmosphere is neither absolute dry nor saturated, it is moist but not saturated, and the generalized potential temperature (GPT) was thus introduced to describe this humid feature of the real moist atmosphere. Comparisons between the GPT in the moist atmosphere and the potential temperature (PT) in the dry atmosphere and the equivalent potential temperature (EPT) in the saturated moist atmosphere were done by analyzing three torrential rain cases occurred respectively over the ChangjiangHuaihe River Basins in 2003 and the north China in 2004 as well as during Typhoon Billis (2006) occurred in 2006. The results showed that the relative humidity is not up to 100% even in torrential rain and typhoon systems, and the saturated condition for defining the EPT is not met completely. The GPT can represent the PT for all of these three atmospheric statuses of dry air, unsaturated moist air and saturated moist atmosphere with the dry or saturated atmosphere being a special case of the GPT. When specific humidity is zero, the GPT becomes PT, and when the specific humidity is up to the saturated specific humidity, the GPT represents the EPT. In addition to linking the PT with the EPT, the GPT can describe the moist concentration and moist gradient better than the EPT. The GPT’s definition included the process that the air changed from dry to moist, then up to saturated, and it can reflect a variety of processes of water vapor giving a better expression to the real moist atmosphere.