Abstract: The distribution，type，composition and formation cause of slag inclusion on the surface and subsurface of continuous casting SPHC slabs had been researched and discussed through observing metallographic samples by optical microscope，SEM and energy spectrum analysis. The result showed that，the slag inclusion could be classified into four characteristic types with different formation mechanism. Slag entrapment of continuous casting mould powder and big-size deoxidation products dropped out from submersed nozzle sediments were the principal source of slag inclusion in continuous casting SPHC slabs. Raising the cleanliness of molten steel，maintaining the stability of continuous casting，alleviating the fluctuation of liquid level in mould，strengthening the anti-fluctuating ability of molten slag layer were helpful to reduce the incidence of slag inclusion in continuous casting slabs.

Key words: continuous casting slab, surface slag inclusion, subsurface slag inclusion, mould powder