The effects of deoxidization and wire feeding operation on the type of titanium, magnesium and aluminum spinel compound inclusion were investigated in 409L stainless steel production process. Further, the formation mechanism of the compound inclusion was also researched at the same time. The results show that the spherical compound inclusion formed in molten steel presents clearly hierarchy after Ti injection in VOD refining process, where the inclusion size is about 5μm to 10μm. The MgO-Al2O3-TiO2 phase of compound inclusion presents regular configuration. MgO and Al2O3 content in compound inclusion decreases gradually together with CaO and TiO2 content increasing from interior to exterior of inclusion. The biphase structure of MgO·Al2O3-TiO2 will be formed with TiO2 dissolving into MgO·Al2O3. On the condition that Ti content is controlled at 0.25 wt.% together with w(Al)<0.01 wt.%, TiO2 solubility is generally less than 20 wt.% in MgO·Al2O3-yTiO2, as y< 0.44.