In this work, graphene layers on SiO(2)/Si substrate have been chemically decorated by radio frequency hydrogen plasma. Hydrogen coverage investigation by Raman spectroscopy and micro-X-ray photoelectron spectroscopy characterization demonstrates that the hydrogenation of single layer graphene on SiO(2)/Si substrate is much less feasible than that of bilayer and multilayer graphene. Both the hydrogenation and dehydrogenation process of the graphene layers are controlled by the corresponding energy barriers, which show significant dependence on the number of layers. The extent of decorated carbon atoms in graphene layers can be manipulated reversibly up to the saturation coverage, which facilitates engineering of chemically decorated graphene with various functional groups via plasma techniques.