Abstract: For the optimization of ethylene cracking severity，an economical optimal index for ethylene and propylene yields was proposed. Optimization in such an economical index enabled to achieve an optimal cracking severity in Naphtha with different features and operational parameters. The introduction of an idea of receding-horizon optimization enabled to overcome the uncertainty from ethylene-and-propylene yield predictive model and the operating disturbance. Industrial application illustrated that the proposed optimization scheme is feasible and economical.