It is important to guarantee the re-injected water quality for the exploitation of the extra-low permeability oilfield. The produced water analysis demonstrates that the conventional physical-chemical methods can not meet the stable re-injected water requirements,especially the removal of suspended solids. Gas chromatography/mass spectrometry analysis was performed to identify the presence of organic compositions of produced water. The results show that most of organic matters are biodegradable. On this basis,this paper studied the treatment of produced water for extra-low permeability oilfield by coagulation-MBR process,and the re-injected water reached the standard stably and continually. The biological treatment as an environmental friendly method on the produced water of extra-low permeability oilfield is recommended. Biological treatment on produced water of extra-low permeability oilfield can ensure the stable re-injected water and avoid the secondary pollution caused by the addition of chemical agents.