Abstract: The system for treating effluent water coming out from the desalter in accordance with the present invention comprises a slop oil separator 1 for removing oil components in the effluent water from the desalter; a WSR separator 2 for further removing emulsion type oil components using naphtha; a water stripper 4 for removing gas components such as H.sub.2 S and NH.sub.3 in the effluent water discharged from the WSR separator; a reaction tank 5 for reacting organic and/or inorganic impurity matters such as phenols and suspended solids in the effluent water discharged from the water stripper with activated charcoal; and a settling tank 6 in which an agglomerating agent is introduced, thereby precipitating sludge in the lower part of the settling tank. A buffering tank 3 may be installed between a desalter (not shown in FIG. 1) and an oil separator 1 or between a WSR separator 2 and a water stripper 4 to play a role as a buffer for safety in case of an accident in the process.