The traditional solvent extraction leads to a large amount of acid-alkali consumption and saline wastewater discharge. Herein, a new strategy was proposed according to the different extraction ability of Ce(IV) and RE(III) with P507, driven by the oxidation and reduction of Ce. As one of the key procedure, the performance and mechanism of replaced stripping of light rare earth elements (LREEs) by Ce(IV) in nitrate solution was investigated in this study. Pr(III) was selected as the representative element of LREEs for the follow-up experiments. Several operational parameters such as phase ratio, temperature, reaction time, concentration of nitrate and Ce(IV) in aqueous feed, and acidity were investigated. Results indicated that the stripping efficiency of Pr(III) increased significantly with increasing temperature, reaction time and Ce(IV) concentration, while it decreased with the increase of phase ratio. The stripping efficiency of Pr(III) was 98% by 0.56 mol/L Ce(IV) under the optimal conditions, which was higher than that by 1 mol/L HCl solution. This method was generally applicable on the stripping of the other LREEs. The mechanism was explored by slope method and FT-IR spectrometric analysis. The solvation mechanism was carried out, and the key complexes in the organic phase before and after stripping were determined to be Pr(NO3)(HA2)2·(HA) and Ce(NO3)2A2, respectively. From the FT-IR spectrometric analysis, it can be concluded that the H in P-O-H was replaced by the rare earth, which was bonded with P=O. Nitrate was also involved in the reaction because of the presence of the characteristic peaks of nitrate.