The low-lying excited-state properties of the water-solvated UO2Cl2 complexes, i.e., (H2O)nUO2Cl2 (n = 1-3), below 33,000 cm-1, are investigated based on the ab initio NEVPT2 and CCSD(T) with inclusion of scalar relativistic and spin-orbit coupling effects. The simulated luminescence spectral curves agree well with the experimental spectrum in aqueous solution at -120 °C. Water coordination is found to significantly affect the character of luminescent state, which is changed from the 3Φg state in UO2Cl2 to the 3Δg state in (H2O)2,3UO2Cl2. This is distinctly different from the observed unchanged nature of luminescent state in the cases of Ar coordination to UO2Cl2 and H2O coordination to UO2F2 in the previous work. Furthermore, by combining with the theoretical results for the solvated UO2F2 system, the reason why water coordination does not remarkably change the spectral shape of UO2Cl2, as opposed to UO2F2, was explained based on the analysis of two key spectral parameters, O-U-O symmetrical vibrational frequency and U-O bond length elongation. The roles of ligand field and spin-orbit coupling in the determination of luminescent state character and spectral shape in uranyl dihalide complexes are deeply discussed and summarized. These results deepen our understanding of the luminescent properties of uranyl complexes in aqueous solution.