Abstract: The crude lithium phosphate, a by-product of salt lakes, cannot be used as a lithium source for synthesizing lithium iron phosphate due to excessive calcium and magnesium impurities.After the preliminary precipitation to remove impurities, the content of impurity calcium and magnesium is still not up to the standard, and the removal difficulty of calcium and magnesium increases. In this regard, this paper simulated the same proportion of lithium phosphate solution system and studied the adsorption effect of D401 chelating resin on calcium and magnesium by thermodynamics and kinetics. It was found that D401 chelating resin had a high selectivity for calcium and magnesium in the phosphate system, and the adsorption process belonged to single molecular layer adsorption and could be spontaneous. It conformed to the quasi-second-order kinetic model and was controlled by micro-particle diffusion and chemical reactions. When the flow rate of the dynamic adsorption solution was 12 BV/h, the removal rates of Ca and Mg were 66.67% and 70.25%, respectively, and the loss rate of lithium was 1.22%. This study has an important reference value for the deep removal of Ca and Mg impurities in lithium phosphate by D401 chelating resin.