A catalytic system, including trifluoroacetic acid and organic solvent additives, was applied to carry out the Beckmann rearrangement of cyclohexanone oxime to epsilon-caprolactam. High conversion (100 %) and high selectivity to caprolactam ([ 99 %) have been successfully obtained using acetonitrile as the additive. The effect of several organic solvents on the reaction was investigated, and the catalyst composition was optimized. The results indicate that the catalytic system with 10 wt% of acetonitrile can give the fastest reaction rate. An immiscible two-phase system was proposed to study the side reaction of oxime hydrolysis which determines the selectivity. Based on the results, a simplified reaction process was suggested and a mathematical kinetic model was developed. The performance of the catalytic system is much better than the classic process. Neutralization agent and ammonium sulfate by-product are both completely avoided.