Azotobacteria N2106,P-releasing bacteria P1616 and K-releasing bacteria K0405 with the functions of N-fixing,P-releasing and K-releasing respectively were isolated from wheat rhizosphere.N2106-L and KL0405 were gained by fluorescence enzyme gene LuxAB transferred into N2106 and K0405.The above five strains were cultured and counted the cell density independently.Then every strain were mixed cultured in equal number in liquid.To study the interactions of these strains,three different combinations were set up: N2106-L P1616, N2106-L K0405,KL0405 P1616 and N2106-L KL0405 P1616.It indicated that the cell densities of the labelled strains were lower than that of the original strains by 1 magnitude;When two strains mixed cultured,P1616 promoted the growth of N2106-L and KL0405 and interaction exist between N2106-L and K0405;When three strains mixed cultured,P1616 was dominant bacteria in liquid culture.