Abstract: A full scale water modeling experiment was carried out for slag entrapment in a CSP funnel-shaped mould with a bifurcated SEN. The structures of the mould and SEN cause meniscus dynamic distortion phenomena of the free surface in the mould which result in periodical mould slag entrapment. The emergent distortion of the bath surface causes short time continuous entrapment by shear force and the appearance of entrapping effectual vortices. Among casting parameters, casting speed has the greatest influence on slag entrapment. The transient behaviors of movement of entrapped slag drops in the CSP mould were also studied. It is shown that periodical slag entrapment leads to a larger distribution difference of large inclusions in the casting direction of slabs.