As an environmental-friendly solvent, methyl-ethyl-ketone (MEK) is the best alternative of pure benzene, toluene and acetone, etc. The producing capacity of MEK has shown an annual increase of 37% in recent 10 years in China. Using mixed C4 to produce MEK has great importance in improving the use of C4 fractions in China, where it is often used as fuels, and the utilization in secondary process is less than 30%. In developed countries this ratio can reach up to 70%-90%. This technology narrows the gap between developing and developed countries.