Fluorinated graphene is one of the most important two-dimensional carbon nanomaterials derived from graphene, and possesses specific and outstanding properties. However, it lacks a cost-effective and large-scale preparation method. Here, we describe a novel and facile solution approach using graphene oxide (GO) and liquid diethylaminosulfur trifluoride as starting materials under mild conditions. The chemical composition and the structure of so-prepared fluorinated graphene were characterized in detail by elemental analysis, solid state F-19 NMR, XPS, FT-IR, Raman, SEM, TEM, and AFM. These studies reveal that some oxygen-containing moieties in GO are converted into C-F bonds, while some are eliminated during the reaction. More interestingly, the fluorine-loading amount can be well tuned by simply altering the reaction medium, and has a significant impact on the optical, electronic, and conductive properties of the product. Preliminary experiments on its application as an electrode material for solid-state supercapacitors were finally presented.