Abstract: The behavior of inclusions during calcium treatment of SPHC steel has been researched by systematic sampling during the process of refining and continuous casting.The results show that before Ca treatment,the Al₂O₃inclusions in steel mainly exist in triangular or irregular forms.After LF refining, most of inclusions are calcium aluminates which have been partly or completely modified.In the tundish, pure CaS forms and binds with calcium aluminates.As the continuous casting of steel proceeds,the proportion of sulfide inclusions increases and more CaS inclusions generate in strands which form annular structures wrapping modified calcium aluminates.