Abstract: To enhance phosphorus recovery efficiency and the resource value of products from swine wastewater anaerobic digestate, this study systematically investigated the influence mechanisms of carbonate (\mathrmCO_3^2- ) and calcium ions (Ca²⁺) on phosphorus removal via magnesium ammonium phosphate (MAP) crystallization using synthetic swine wastewater anaerobic digestate. Batch precipitation experiments, coupled with Visual MINTEQ 3.0 thermodynamic modeling and X-ray diffraction analysis, were conducted to elucidate the phosphorus removal behavior and product characteristics under different pH conditions and molar ratios of n(Mg)∶n(N)∶n(P). The results indicated that a phosphorus removal rate exceeding 96% was achieved at pH 9.5 with n(Mg)∶n(P) = 1.4∶1; further increases in pH or n(Mg)∶n(P) molar ratio showed no significant improvement in removal efficiency. The presence of \mathrmCO_3^2- alone had minimal impact on phosphorus removal (>95%) and the purity of MAP crystals. In contrast, the presence of Ca²⁺ alone significantly altered the composition of the precipitates. When n(Mg²⁺)∶n(Ca²⁺) = 2∶1, the purity of MAP was approximately 66.7%, and as the Ca²⁺ concentration increased, the products gradually transitioned to being dominated by amorphous calcium phosphate. The combined influence of \mathrmCO_3^2- and Ca²⁺ was largely consistent with that of Ca²⁺ alone. Under high Ca²⁺/\mathrmCO_3^2- conditions, although a high phosphorus removal rate (≥95%) was maintained, the purity of the product decreased substantially. In practical applications, the Mg∶P molar ratio should be precisely controlled based on the ionic concentration ratios to balance phosphorus removal efficiency and the resource value of the recovered products.