Graphene oxide (GO) sheets with controlled species of oxygen-containing groups are important for fabricating graphene materials with desired structures and properties. Here we report a water-addition modified Hummers method to prepare GO sheets with tunable amounts of hydroxyl and epoxide groups without destroying their structural integrity. This method is simple, effective, and efficient. It can be applied to the mass-production of GO with controlled amounts and species of oxygenated groups, and improve the yields of synthesizing high-quality GO at low temperatures.