The accumulation of inclusions in the initial solidified shell, which may cause longitudinal cracks, is studied in this paper. The composition, morphology and distribution of large inclusions in thin slab are investigated by inclusion measurements. Based on the experiment, the quantity and size distribution of inclusions are obtained as reference in predicting inclusion behavior in CSP mold through numerical simulation. Due to the funnel-shaped structure of mold, inclusions injected through SEN are mostly captured by the solidifying shell in the funnel region nearby the parallel part of mold, which cause the accumulation of inclusions in thin slab within this region. Moreover, the simulation results are consistent with experimental data that large inclusions concentrate at the position of 1/4 slab width, which suggests a lower product quality there. In addition, the distribution of inclusions in the solidified shell is closely related to their motion in the mold. Specifically, the transport and removal of inclusions entrained from mold slag are calculated, since K/Na-contained inclusions and excessive surface velocity demonstrate that slag entrainment appears in CSP mold. These inclusions can float up easily, while those entrapped by the shell are detrimental to thin slab quality.