P507 (HEH[EHP]) is an important extractant for the separation of rare earth and is widely used in industry. Since the complexes of heavy rare earth ions with saponified P507 are so stable that the rare earth ions are difficult to be exchanged and stripped by H+ ions. Thus, the cycled extractant loads certain amount of heavy rare earth ion after stripped by acid. This amount of rare earth ions loaded in blank organic phase is named as the “cycling loaded rare earth ions (CLREs)”. In the separation process of Tm 3+ , Yb 3+ , and Lu 3+ , the amount of CLREs can be more than 10% of the normal capacity of saponified organic phase. In fact, CLREs affect the separation efficiency and decrease the purity of the products. Based on the extracting-stripping equilibrium and mass balance, the influence of different process parameters on the amount of CLREs was studied by computer simulation. The results indicate that higher acid consumption and more stripping stages are required to eliminate CLREs. For an industrial practice, however, the acid consumption and the number of stripping stage can be designed by choosing an economic process and controlling CLREs at a reasonable level. P507 (HEH [EHP]) is an important extractant for the separation of rare earth and is widely used in industry. Since the complexes of heavy rare earth ions with saponified P507 are so stable that the rare earth ions are difficult to be be exchanged and stripped By H + ions. Thus, the cycled extractant loads certain amount of heavy rare earth ion after stripped by acid. This amount of rare earth ions loaded in blank organic phase is named as the “cycling loaded rare earth ions (CLREs).” In the separation process of Tm 3+, Yb 3+, and Lu 3+, the amount of CLREs can be more than 10% of the normal capacity of saponified organic phase. In fact, CLREs affect the separation efficiency and decrease the purity of the products Based on the extracting-stripping equilibrium and mass balance, the influence of different process parameters on the amount of CLREs was studied by computer simulation. The results indicate that higher acid consumption and more stripping stages are required to eliminate CL REs. For an industrial practice, however, the acid consumption and the number of stripping stages can be designed by choosing an economic process and controlling CLREs at a reasonable level.