For a highly efficient recycling of a wastewater containing a high concentration of MgCl₂, Al(III) and P507 were scheduled to be removed in advance. In this study, the in-situ removal of Al(III) and P507 from a high concentration MgCl₂ solution at different pH values and Al/P molar ratios was investigated. The results showed that P507 formed organic complexes of Al_x(OH)_y^z+-P507 at pH of 2.0-4.0. At pH of 4.0-5.0, Al(III) precipitated and transferred into Al(OH)₃ with a flocculent amorphous morphology. Active sites on the Al(OH)₃ surface enhanced the removal efficiency of P507. At pH of 6.0-6.5, Al(III) and Mg(II) formed layered crystalline Al(OH)₃ and MgAl₂(OH)₈ with small pore channels and fewer active sites, resulting in a reduced removal efficiency of P507. When the Al/P molar ratio exceeded 13 and the pH was between 4.0 and 5.0, the removal rates of both Al(III) and P507 were higher than 98%, while the concentration loss of Mg(II) was only 0.2%-0.9%.