This study aimed at revealing the mechanism of calcium-magnesium phosphate fertilizer (CMP) mobilization the mechanism of starter phosphorus (P) addition on affecting CMP utilization in maize rhizosphere in a calcareous soil.Different starter P in the form of KH2PO4 (0, 8 and 15 mg P kg−1 soil) and CMP (0, 100 and 500 mg P kg−1 soil) were set up to determine the CMP utilization efficiency of maize. The shoot dry weight, shoot P content, soil Olsen-P and soil carboxylates concentration were measured. Correlation analysis was performed to reveal the function of carboxylate on CMP mobilization.The application of CMP significantly increased the maize shoot dry weight and P content, and the combined application of starter P and CMP significantly improved the effect of CMP on maize growth. Especially, when CMP was added at 100 mg P kg−1soil and KH2PO4 was added at 8 mg P kg−1 soil, root fresh weight, rhizosphere soil Olsen-P, shoot dry weight and shoot P content significantly increased by 35.4%, 63.2%, 69.7% and 70.8%, respectively. The mobilization of CMP was mainly related to the concentration of succinate and T-aconitate in the rhizosphere. Moreover, the addition of 8 mg P kg−1 soil starter P enhanced succinate and T-aconitate concentration and improve CMP utilization under 100 mg P kg−1. This study indicated that succinate and T-aconitate secreted by maize promoted the mobilization and utilization of CMP and the combined application of CMP with starter P enhanced CMP fertilizer utilization in a calcareous soil.