Abstract: To most of the high water containing oilfields, improving the effect of water injection is urgently solving problem. The mi-croorganism which grows and metabolizes in water can solve the problem by reducing the pH value of water and generate biologi-cal acid to enhance the acidity of water. The biological polymer produced by microorganism can increase the viscosity of water
phase, so as to improve the sweep factor and reduce the ratio of water and oil. Meanwhile, the chemical precipitation by the combination of the growing bacteria and its metabolite and heavy-metal may form physical plug, so as to adjust the water injec-lion section, selectively seal the underground water and change the direction of flowed water. The bacteria may get into forma-
lion and generate chemical precipitation in the throats and pores.Therefore，it could effectively seal the pores of water containing formation. Also, it is helpful to reduce the water influx.

Key words: microorganism for oil recovery, functional mechanism. undeground and water, constructed experiment, sweep factor, effect of water injection