Nozzle clogging is serious problem for steel continuous casting, especially for low-aluminium killed steel. For the submerged-entry nozzle (SEN) clogging process, previous studies often adopt experimental means to analysis type, morphology and composition of the clogging materials, and then to speculate and to verify the thermodynamic mechanism, a lot of previous research in this area has been done. Nozzle Clogging is a complex process containing thermodynamics and kinetics of physical processes and chemical processes. In current paper, with the help of experimental means such as optical microscope, scanning electron microscopy and transmission electron microscopy, SEN clogging material morphology and composition have been investigated. Effect of decarburization reaction layer on the initiation process of nozzle clogging has been investigated. The kinetic condition of inclusions adhesion to nozzle wall is also been discussed.