The work function modulations of AuCl4 -graphene system have been theoretically investigated. The calculated results of work function modulations are in agreement with the recent experiment [ACS Nano, 4(5) (2010) 2689]. However, the theoretical works are lack for revealing the mechanism of the work function modulation in AuCl4 -graphene system. Our simulation reveals the work function can be modulated by the adsorbed concentration. It should be originated from the Fermi level shifting and the emergence of charge redistribution. The behavior of charge redistribution can result in the enhancement of the surface dipole and further the modulation of the work function. (C) 2011 Elsevier B.V. All rights reserved.