Abstract: In this paper, we used alfalfa and acid tolerate alfalfa rhizobium stain, Sinorhizobium meliloti 91522, as materials in water culture to study the effect of calcium and phosphorus on quorum sensing (QS) and N-fixation of alfalfa-rhizobia after acid aluminum stress. The research showed that calcium and phosphorus could repair the symbiosis nodular process of alfalfa-rhizobia after suffering from acid and Al toxicity; comparing with the control treatment, which is no Ca²⁺ and P treatment, under the conditions of 10 mmol/L Ca²⁺ and 4 μmol/L P, the nodulation time was 14 days earlier, nodular number had increased by 247.09%, the nodular ratio achieved to 90%, hair deformation rate of Medicago sativa increased from 3.33% to 28.89%. When 10 mmol/L Ca²⁺ and 4 μmol/L P were added, the nitrogenase activity improved significantly, and Ca²⁺could enhance the QS of S. meliloti significantly as well, hence promoting alfalfa to perceive the nodular signal. Preliminary tests proved that Ca²⁺ and P could recover the symbiosis nodular process and nitrogenase activity after alfalfa suffered from acidity and Al toxicity.