Bilayer graphene has attracted a great deal of attention for many electronic and optical applications. Although large-area bilayer graphene can be synthesized by chemical vapor deposition (CVD), multilayer growth often occurs and subsequent processes are required to obtain uniform bilayer films. We report an efficient way of thinning multilayer graphene film by low-power CO2 laser irradiation in vacuum. With a laser power density of ~10(2) W cm(-2), pristine graphene film of 4-5 layers can be thinned to a bilayer free of defects in 30 s. Contrary to previous laser-assisted graphene thinning processes, which reduced graphene layers precisely and locally with a high power density and a small beam diameter, our approach enables high-efficiency thinning of large-area graphene film whilst using a significantly reduced power density and an increased laser beam diameter.