The increase of Al content and change of inclusion composition is occurred for Sikilled or lightly Alkilled steels in LF process. Factors related to increase ot Al content such as refining slag compositions,molten steel composition LF refining time etc.were studied theoretic ally and practicaley. The practical result shows that the Al content is hardly increased during LF treatment with CaOSiO2 refining slag, but Al content is increased at different degree with refining time for different steel grades with CaOAl2O3 refining slag, and the trend is nearly consistent with theoretical calculation,Comparing with CaOSiO2 refining slag, the content of Al2O3 inclusion increases 4 times, and in complex oxide inclusions the Al2O3 content increasesly 113%, and the CaO increases by 24.5% respectively duriug LD treatment with CaOAl2O3 refining stag.Applying the result to practical production of tire wire steel 72A and other steels, it is able to control Al under 0.0005% for 72A and under 0.003% for other steels in LF refining process to avoid forming harmful inclusion and eliminate the nozzle clogging.