Abstract: This study aims to explore the effects of inoculating arbuscular mycorrhizae fungi (AMF) and phosphate solubilizing bacteria (PSB) on the dry matter yield of alfalfa, and phosphorus use efficiency under various treatments with different phosphorus level, and thereby an optimal fertilization mode was established for the selected alfalfa. A randomized block design was used in the experiment for two factors of bacteria and phosphorus. Four levels of phosphorus application were set, including 0 (P0), 50 (P1), 100 (P2), and 150 mg/kg (P3). Four types of inoculation treatments were as follows: no inoculation (J0), Funneliformis mosseae (J1), Bacillus megaterium (J2), and double inoculation (B. megaterium + F. mosseae) (J3). Sixteen treatments were set, each of which was repeated six times. The treatment group was inoculated with Funneliformis mosseae, where the average amount of fungus was 10 g/pot. In the treatment group of Bacillus megaterium, the average amount of bacterial solution was 10 mL/pot. In the mixed inoculation group, Bacillus megaterium in each pot was added the amount of 5 g (about 8 500 inoculation potential units) and 5 mL. The same number of sterilized bacteria was also added to the J0 treatment. The results showed that the dry matter yield of alfalfa at the total or individual cut gradually increased first and then decreased, with the increase in the application rate of phosphorus under the same conditions of bacteria treatment. In the J3 treatment, the total dry matter yield of alfalfa reached the maximum under the P1 phosphorus level. In the rest of bacteria application conditions, the total dry matter yield of alfalfa reached the maximum in P2 phosphorus level. The phosphorus content of aboveground plants increased first and then decreased, as the application rate of phosphorus increased. Specifically, the content of phosphorus in treatment group was significantly higher than that in the non-phosphorus treatment (P<0.05), whereas, there was no significant difference between phosphorus application treatments (P>0.05). The partial productivity and agronomic efficiency of phosphorus fertilizer decreased, with the increase of phosphorus application rate. The contents of total phosphorus (TP) and rapid available phosphorus (AP) increased in rhizosphere soil and non-rhizosphere soil, with the increase in the application rate of phosphorus. In the same phosphorus conditions, the dry matter yield, phosphorus content of plant, use efficiency of phosphorus, TP, and AP content of alfalfa under the single or mixed inoculation treatments were significantly higher than those under non-inoculation treatment (P<0.05), where the contents of TP and AP reached the maximum in the J3 treatment. There was the highest correlation coefficient between the AP content in rhizosphere soil and dry matter yield, indicating the optimal fitting effect. The contents of TP and AP were positively correlated with the total dry matter yield. Therefore, when the application rate of phosphorus was set as 100 mg/kg, the comprehensive inoculation of AMF and PSB can significantly increase the phosphorus availability in soil, thereby to improve phosphorus use efficiency, further to increase the dry matter yield of alfalfa. The finding can provide a theoretical basis for the high production of alfalfa, and the application of efficient compound microbial fertilizer.