Abstract: The relationship between the size distribution of inclusions and the total oxygen in steel was studied by following the inclusions' size and number of the samples at different locations. The content of macro-inclusions in liquid steel could be estimated accurately by the fluctuation of total oxygen in the same sample,which quantified the cleanliness evaluation index. The number of inclusions per unit volume decreased exponentially with the increase in sizes. Also,the distribution uniformity of inclusions in steel worsened as the size increased. Thus,micro-inclusions with the size below 10 μm occupied above 95% of total inclusions in the liquid steel,which showed a good relationship between the measured value of total oxygen and the integration oxygen in micro-inclusions.Total oxygen could represent the uniform distribution level of inclusions in steel; good uniform of inclusions in steel meant small fluctuation. Macro-inclusions could result in the fluctuation of total oxygen. Large fluctuation of total oxygen reflected a high amount of macro-inclusions in steel.