Disclosed is a PDP driving method and a plasma display device for providing stable discharge characteristics by varying gradients of PDP driving waveforms according to the external temperature of the PDP. A protection film of MgO reduces the secondary emission coefficient as the temperature is reduced. In order to compensate for the reduction, the external temperature is measured by an external temperature sensor, and the gradients in a falling period and/or the rising period during a reset period of a driving voltage waveform are modified according to the measured external temperature. In detail, the gradients in the falling period and/or the rising period of the reset period are varied to be less steep when the measured temperature is reduced to below a predetermined level such as freezing or −10 degrees C.