Sc (0, 1, 2, 3 mol%): Tm: LiNbO3 crystals were prepared by the Czochralski method. The inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis test shows that, as the concentration of Sc3+3+ increases, the effective segregation coefficient of Sc3+3+ and Tm3+3+ decreases. The X-ray diffraction (XRD) analysis test shows that the lattice size increases first and then decreases. The optical homogeneity analysis test shows that the birefringence gradient of the Sc-3 sample is 4.7×10−54.7×10−5ΔΔR/cm−1−1, which is 1/3 of pure LiNbO3. Research demonstrates that when the Sc3+3+ content reaches or exceeds the threshold value, Nb4+LiNb4+Li is replaced completely, thus introducing non-intrinsic defects Sc2+LiSc2+Li and Sc2−NbSc2−Nb. These defects are able to form Sc2+Li−Sc2−NbSc2+Li−Sc2−Nb charge self-compensating defect groups, it will greatly increase optical homogeneity.