Beckmann rearrangement mechanism of cyclohexanone oxime, based on the characteristic of self-catalyzed reaction and polymorphism was proposed. According to the suggested mechanism, the basic approach was the rearrangement of OXH~+ while the SO_3 acts as dehydrating agent and OXSO_3 can turn to CPLSO_3 ultimately. Considering self-catalyzed reaction between OXSO_3 and CPLH~+, kinetic model for Beckmann rearrangement was established. Corresponding parameters were estimated by using float genetic algorithm (GA) and simulation results agree well with the experimental data below -19.3℃. Industrial equipment was simulated and analyzed. Effects of key process parameters such as molar ratio of sulfuric acid to oxime and circulation ratio on the residual oxime are also discussed. The results show that the caprolactam exists as CPLH~+ finally in oleum and the minimum molecular ratio of sulfuric acid to oxime can be 0.5 theoretically. Beckmann rearrangement mechanism of cyclohexanone oxime, based on the characteristic of self-catalyzed reaction and polymorphism was proposed. According to the suggested mechanism, the basic approach was the rearrangement of OXH ~ + while the SO_3 acts as dehydrating agent and OXSO_3 can turn to CPLSO_3 ultimately. Considering parameters were estimated by using float genetic algorithm (GA) and simulation results agree well with the experimental data below -19.3 ℃. Industrial effects of key process parameters such as molar ratio of sulfuric acid to oxime and circulation ratio on the residual oxime are also discussed. The results show that the caprolactam exists as CPLH ~ + finally in oleum and the minimum molecular ratio of sulfuric acid to oxime can be 0.5 theoretically.