Abstract: Four PGPRs (plant growth promoting rhizobacteria) were isolated and screened from the rhizospheres of Medicago sativa, Trifolium repens and Trifolium pratense. Antagonistic reactions, the ability of solubilizing phosphate and the production of IAA (Indoleacetic Acid) by strains in both single and compound culture, together with the pH values of culture solutions and total contents of organic acid were tested. The ability to solubilize phosphate and produce IAA were determined by molybdenum-bule and Salkowski colorimetry. The relativity of isolated bacterial strains was analyzed. The results showed that there was no antagonistic reaction between different single strains so that compound strains could be utilized. In a bio-phosphorus culture solution, the Hsg+lhs11 compound strain had the highest increment of effective-phosphorus (536.2 mg/L), while the Hsg+ls1-3+lhs11 compound strain was second (475.6 mg/L). Effective-phosphorus increments gave additional effects of “1+1>2” in Hsg+lhs11 compound strains. Effective-phosphorus increased in Hsg+ls1-3+lhs11 compounding strains compared with single strain treatmenst (P<0.01), but there was no additional effect with “1+1+1>3” Hsg+ls1-3+lhs11 compound strains. In organic phosphorus culture solution, the lhs11 strain had the highest effective-phosphorus increment (11.11 mg/L), and Hsg+ls1-3+lhs11 compound strains was second (9.20 mg/L). The effective-phosphorus increment with the Hsg+ls1-3+lhs11 compound strains was higher than in other compounding treatments. There were linear correlations between effective-phosphorus increment and pH value, effective phosphorus increment and total content of organic acid, pH value and total content of organic acid. Single strains and compound strains both had the ability to produce IAA, between 0.212-9.331 mg/L. The IAA content in the Hsg+lhs11 compound treatment was higher than that of the single strain Hsg or lhs11 treatments (P<0.01), both of which presented a “1+1>2” additional effect. Consider the growth-promoting effects of different treatments, the Hsg+lhs11 compound strains and Hsg+ls1-3+lhs11 compound strains had better interaction effects so they have the potential to develop the optimal compound strain fertilizer.