The Ce3+ ions occupying the two crystallographically distinct Y3+ sites both with C, point group symmetry in the X2-Y2SiO5 (X2-YSO) crystal are discriminated by their spectroscopic properties calculated with ab initio approaches and phenomenological model analyses. Density functional theory (DFT) calculations with the supercell approach are performed to obtain the local structures of Ce3+, based on which the wave function-based embedded cluster calculations at the CASSCF/CASPT2 level are carried out to derive the 4f -> 5d transition energies. From the ab initio calculated energy levels and wave functions, the crystal-field parameters (CFPs) and the anisotropic g-factor tensors of Ce3+ are extracted. The theoretical results agree well with available experimental data. The structural and spectroscopic properties for the two types of Ce3+ ions in X2-YSO are thus distinguished in terms of the calculated local atomic structures, 4f > 5d transition energies, and spectral parameters.