Abstract: In the current paper, several projects on non-metallic inclusions in steel that are still not well solved and clarified are discussed, including the detection of the three-dimensional morphology of inclusions, thermodynamics of deoxidation using multiple deoxidizers, calcium treatment of the molten steel, the dependence of the deformation ability of inclusions on their melting temperature and composition, the effect of alloys and added materials on the composition of inclusions, the clogging mechanism of the submerged entry nozzle during continuous casting, the mechanism of the erosion reaction between molten steel and lining refractory, the kinetics of the size and composition of inclusions and coupled with the fluid flow in the metallurgical vessel during steel refining and casting process. The projects above are the key problems of inclusions in steel. If these projects are solved within next 5-10 years and used in steel production process, the quality of steel can be well improved.