Abstract: Proposes a three level flowsheeting strategy for the flowsheets with inlay feedback loops, based on simultaneous modular strategy first explored by Rosen. The three level flowsheeting strategy can be successfully used in methanol synthesis flowsheeting with inlay feedback loops, and in contrast to Rosen's method, it can reduce largely the CPU time in flowsheeting. The methanol synthesis flowsheeting system compares favorably with the industrial prototype and has the role for directing industrial production.