Abstract: Traditional optimization strategy for crude distillation units is generally based on the feasible path method,which has low optimizing efficiency because of complexity of distillation model.Direct infeasible path method for the units has very high dimensions which cause difficulty in converging.According to the properties of crude distillation model,an IOIPO(Inside-Out Infeasible Path Optimization) algorithm is proposed by combining of inside-out simulation method of distillation column and infeasible path method of optimization.In this algorithm,residual equations of energy balance converge within optimization layer,which means simulation convergence in each optimization is not required,meanwhile in optimization layer only a few constraint equations are added in,so that the IOIPO method can greatly raise converging speed and reduce computational time.It will be very useful for on-line optimization of crude distillation units.