Through this study, we have completed the simulation of dimethyl ether (DME) separation process as diesel alternative fuel Aspen Plus release 12.1. We used NRTL liquid activity coefficient model to describe the vapor-liquid equilibrium phase behavior for mixtures and used Henry's law option to explain the solubilities of inert gases with water and methanol solvents. DME separation process consists of four columns, one is an absorber and the three distillation columns. In this work, we concluded that DME product having 99.9 mole percent purity could be obtained by using four-column configuration.