Abstract: The size,distribuing density,shape and amount of inclusion in Q235B liquid steel were analyzed by metallographic examination. The results show that the size and amount of small particle inclusion were increased after refining. However,＞20 μm globular and similar globular and non-globular inclusion were reduced to 43%. The size and amount of non-globular inclusion were reduced greatly,and the proportion of globular and similar globular inclusion were lifted to 40%. And the size and amount of ＞50 μm inclusion were also reduced. The effect was obtained to changed size and distribution density of inclusion by refining composition slag.