Washing oil, one of the important distillation cut of coal tar, consists of a series of high value-added components which can form azetropic and eutectic system, making it impossible to separate certain components completely by normal distillation. In this work, a scheme coupling distillation with crystallization to deal with this cut for pure chemicals is simulatively investigated before an industrial design. By the aid of this research, a 25Kt/a pilot scale unit was successfully designed which is now running with α-methyl-naphthalene, β-methyl-naphthalene, fluorene, dibenzofuran and acenaphthylene in high purity as main products and naphthalene fraction, medium washing oil (dimethylnaphthalene) and heavy washing oil as by-products.