Abstract: Interaction between chlorella vulgaris and two strains of marine heterotrophic bacteria(Z-QD08 and Z-QS01) was studied. Z-QS01 showed inhibitory effect on C vulgaris and the inhibitory effect was enhanced gradually with increasing density of Z-QS01. Z-QD08 stimulated the growth of C vulgaris at low density, and presented an inhibitory effect when the density of Z-QD08 reached 10⁷cells/mL. There were obvious different effects on C vulgaris among different compounding ratio groups of Z-QD08 and Z-QS01 in the initial phase. The dominant group of Z-QS01 restrained the growth of C vulgaris, while the dominant group of Z-QD08 and equivalent group showed stimulative effects to C vulgaris. Yet all groups showed stimulative effects to C vulgaris in the terminal phase. C vulgaris decreased the cell density of Z-QS01 while stimulated the growth of Z-QD08 in the exponential growth phase. C vulgaris demonstrated selective inhibitory effect to Z-QS01 in the mixed culture system. Experimental results offered theoretical support to apply ecological control in marine culture and to develop microbial preparation.