The invention relates to an electric-coagulation oil-water-sedimentation separation device used for carrying out oil-water-impurity separation of oil field produced water. The device comprises a horizontal tank body. The inside of the tank boxy is sequentially divided into an inlet water heating buffering zone, an electrostatic separation zone, an inclined plate oil-removing zone, an air floatation zone, and an outlet water buffering zone. The air floatation zone is divided into an air floatation contact zone and an air floatation separation zone. An air-discharge pipe is arranged on the top of the tank body. An oil-discharge pipe is arranged on the upper part of the tank wall. A hot water pipe and a water return pipe are arranged at reservoir close to the oil-discharge pipe. A perforated sludge-discharge pipe is arranged on the lower part in the tank, and is connected with a sludge-discharge manifold through a valve. Waste-discharge pipes are respectively arranged on pipe lower walls corresponding to the inlet water heating buffering zone, the electrostatic separation zone, the inclined plate oil-removing zone, the air floatation zone, and the outlet water buffering zone. The waste-discharge pipes are connected to the sludge-discharge manifold through valves. With the processing of the device, effective oil-water-solid impurity separation can be performed to water, and the water can satisfy an inlet water quality standard requirement of the next stage of filtering.