A one-dimensional fluid model is developed for describing the pulse-modulated radio-frequency glow discharges in atmospheric helium. The influences of the duty cycle of modulation pulses on the characteristics of discharge are studied. The numerical results show that there are two different regimes with reducing duty cycle, and that in each regime, the dependence is linear. The reason for it is the residual electrons in the electrode gap, which play an important role during the plasma ignition phase. It is consistent with the experimental study. (C) 2011 Elsevier B.V. All rights reserved.