In this paper, the raising voltage process is defined as stepping up the applied voltage, whereas the reducing voltage process means turning down the applied voltage, which follow on the termination of the raising voltage process. Discharge images, the waveforms of applied voltage and discharge current, Lissajous figures, and the optical emission spectra of the two different processes were acquired in needle-plate alternating current dielectric barrier discharge in humid nitrogen at atmospheric pressure. Conclusively, the characteristics of the discharges with the same applied voltage in the raising and reducing voltage processes are pretty different. The discharge in the reducing voltage process is more intense and the power consumption is about three times than that in the raising voltage process at the same applied voltage. Analysis shows that the phenomena would be interpreted by the effect of the space charges in the discharge gap, and worth taking more efforts in the practical applications.