The constructed wetland is an ecological sewage treatment with good purification effects and low construction and operation costs.  However,  the oxygen condition in constructed wetlands is of particularity and affects purification efficiency of wetlands.  For the lack of systematical study on oxygen condition of wetlands,  the further development of wetlands is restricted to some extent.  In this paper,  the intensifying measures of oxygen condition in horizontal flow wetlands were studied,  the optimal operation condition of them were determined.  Operation in series,  aerifying and multi-inflow and circmfluence were studied by experiments.  The results show that operation in series improved oxygen condition unconspicuously.  Oxygen concentration in aeration wetlands and multi-inflow wetlands were improved.  The optimal gas-flow ratio was 4~5.  And the assigned ratio of inflow was 1∶2∶1.  The results of research demonstrate that circumfluence makes purifying effect of constructed wetlands improved obviously.  Removal efficiency of various pollutants increases quickly.