Abstract: This article reports the flow characteristics and oxygen-enriched effect of round outlet oxygen diffusion at a large space.Experimental results show that the axial maximum velocity and oxygen concentration of oxygen diffusion both decrease with axial distance,and there are large velocity and oxygen concentration gradients within an axial direction range of 0 to 0.6 m. The oxygenenriched regions are similar at different outflow velocities and their concentration profiles are closer to a semi-elliptical form by a smaller outlet diameter at the downstream,which contributes to forming a much larger oxygen-enriched region. A relation between the extended half-width of outer boundary enriched area and the axial distance and a relationship between the oxygen-enriched area and the outflow rate are obtained through function fitting. The oxygen-enriched area formed by dual outlet oxygen diffusion approximately decreases 10% than that by single outlet oxygen diffusion with the same outflow rate; the oxygen-enriched area formed by 6 mmdiameter outlet oxygen diffusion increases about 10% compared to 8 mm-diameter outlet oxygen diffusion.