is necessary for the synthesis of the process separating a raw material into multicomponent products to consider the degrees of separation sharpness and the stream division ratios as design variables in addition to the separation sequence. It is difficult to synthesize this separation process optimally because there is information feedback between the separation sequence, stream division and separation sharpness. A useful method of two stages is developed for this synthesis problem. The first stage is to search for the separation sequence, the second stage is to search for these degrees and ratios, and these two stages are repeated until the optimal separation process is synthesized. It is found that the configuration constructed by manipulating the modified material allocation diagram is suitable for the initial one, that the ratios can be determined by solving the material balance equations when the degrees are known, and that material balance equations become linear by adopting the relative flow rates allocated from the outflowing streams to the products as the variables. These equations can be solved separately for individual products, so that the calculation load can he greatly reduced. There are often more or less variables than equations. This contradiction can he resolved by decomposing the subproducts further with the minimum increase in the separation mass load and/or adjusting the order of the products in solving the linear equations to supply additional relations between the variables. The proposed method is illustrated through the solution of a fivecomponent five-product distillation separation process synthesis problem.