The invention discloses a halogen-free flame retardant antistatic polycarbonate composition and a preparation method thereof. The composition comprises the components based on parts by weight: 50-70 parts of polycarbonate, 5-20 parts of polymer which can form a third phase, 8-15 parts of impact modifier, 3-15 parts of phosphonium flame retardant, 0.2 part of fluoro-polyolefine additive, 1-10 parts of conducting material and 0.1-1 part of other accessory ingredient. When in operation, the polymer which can form the third phase, the phosphonium flame retardant, the conducting material and other accessory ingredient are firstly melted and extruded by a double screw extruder to prepare intermediate composition; after being melted and extruded by the double screw extruder, the intermediate composition, the polycarbonate, the impact modifier and the fluoro-polyolefine additive are pelleted and then dried. The composition prepared by the invention does not contain chlorine and bromine, has excellent antistatic property, flame retardance, impact resistance and formability and needs a little conductive filler.