In this paper, the results of a study on the influences of different morphologies, types, and sizes of inclusions on the fatigue lives of 20CrMnTi are reported. The results show that the addition of the rare earth element Ce can lead to the formation of spherical CeAlO3-TiN inclusions in 20CrMnTi. The fatigue performance of 20CrMnTi-Ce was significantly improved compared to that of 20CrMnTi. Using the “edge-to-edge matching” crystallographic theory, CeAlO3 was validated as a suitable hetero-nucleus core for TiN, and the following best orientation relationships between them were determined: [010]TiN//[21¯1¯1] CeAlO3&(002) TiN//(112¯1)CeAlO3. The fatigue cycle times of 20CrMnTi-Ce range up to 107, and this value is higher than that of 20CrMnTi without Ce. As the size of the TiN inclusions increases, the maximum stress of the steel matrix also increases. Also, the high-stress and low-life regions noticeably increase, thus increasing the possibility of a fatigue fracture. Under the same sizes of inclusions, the high-stress and low-life regions of square TiN are larger than those of circular TiN.