The number， form， composition of inclusion and T［O］ and［N］ content in SPHD steel refined by RH at refinery and continuous casting stage were analyzed by metallographic statistic， SEM， electron probe and N-O analy- zer. The results show that the cleanliness and castability of molten steel could be improved by reducing and avoiding Al-O action during RH refinery. Modifying the inclusion in RH steel and increasing the rising speed of inclusion were the major measures for improving the castability. Reducing the erosion of refractory in tundish and slag entrap- ment avoidance were the important methods for increasing the cleanliness.