Abstract: Based on the theory of cascade extraction, a computer program was established in order to simulate the steady-state behavior of HNO₃, U and Pu in the co-decontamination process in Purex. The reliability of the simulation was verified by the reported parameters. The process security was analyzed and the process parameters were optimized through changing the flow rate and component of the feed stream (1AF), extractant stream (1AX) and scrubbing stream (1AS). It is found that the recovery of uranium and plutonium is remarkably affected by the flow rate change of 1AF and 1AX, slightly by that of 1AS. The increase in the acidity of 1AS can improve the operational flexiblility of 1A while lowering the decontamination of U product over the rare earths.