Abstract: Non-metallic inclusions in the steel for pressure vessels produced through BOF-RH-Continuous Casting technological process were investigated systemically. The morphology, size, composition and origination of the inclusions were analyzed. It is concluded that the inclusions in the slabs are mainly small-sized angular alumina inclusions and alumina clusters (<40 μm), while the larger ones together with the resultants of reaction between ladle slag and molten steel were removed by floating out during casting. The total oxygen of the slab is in the range of (14-16)×10^-6 and the amount of the inclusions in the slabs changes from 0.09 -0. 15 mg/kg, Which indicate the high cleanliness of the slabs.