12% Cr alloy based on iron is usually used for advanced electric rotor shaft which requires very good mechanical property and fine inclusions, as the large-sized inclusions in the alloy usually can cause performance deterioration. In this work, quenching process was adopted after slow cooling experiment in order to retain the inclusions precipitated during melt cooling and solidification of 12% Cr alloy. The morphology and the composition of the inclusions were detected by scanning electronic microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The results show that except various shapes of oxide, typical TiN inclusion is found in the sample. However, there is no Ti added in metallurgical process. Thermodynamic calculation was executed to interpret the inclusion precipitation during solidification and the calculation results indicate that TiN inclusion precipitates at the terminal stage of solidification. Even a trace amount of Ti drawn from raw materials would induce the precipitation of TiN, which would grow into large size and be harmful to alloy property, while the formation of Al₂O₃ inclusion occurred in liquid alloy. Suggestions for the control of Ti and O are given based on the calculation results, which would be helpful to the production of 12% alloy. The precipitation potential of Ti₂O₃ inclusion in the experiment has also been discussed by studying the competition of element concentration between Ti and Al.