C4 mixtures are usually separated by extractive distillation with acetonitrile (ACN) and N,N-dimethylformamide (DMF) methods in industry. These two methods were modified to improve the extractive distillation process in this work. Vapor-liquid equilibrium (VLE) models for the ACN and DMF methods were established with the Wilson equation. In terms of the models the extractive distillation processes were improved by means of a computer simulation software. The improvement to the ACN method was such that liquid load in the second extractive distillation column was significantly decreased and there were few changes on the equipment. Improvement to the DMF method was also made by replacing tray configuration and decreasing the times of butadiene phase changes. Both improvements are closely connected with the C4 practical production and are easily accomplished.