A needle-copper plate device excited by a direct current (DC) voltage is used to produce a nonequilibrium low temperature plasma plume at atmospheric pressure. Through optical method, it is found that the plasma plume discharge is pulsed. The total light emission signal is compared with the emission signal of 337.1 nm spectral line and the discharge current signal, it is found that the pulse duration is the largest for the current signal, and it is the smallest for the emission signal of 337.1 nm spectral line. Furthermore, the discharge frequency is studied, and results show that the discharge frequency increases with increasing the applied voltage. By using a spectrometer, the intensity of 337.1 nm spectral line decreases with increasing gas flow rate. It increases firstly and then decreases with the increasing the voltage. All of these physical phenomena mentioned above are analyzed qualitatively by gas discharge mechanism. These findings are of great importance for the generation and applications of non-equilibrium low temperature plasma plume generated at atmospheric pressure.