Calculations at CCSD(T) theoretical levels with extended basis sets on CO…H2O provide reliable structures and stability, as well as the covalent character of the hydrogen bond. The interactions were decomposed in the framework of symmetry adapted perturbation theory to investigate the HB properties. It demonstrates that the electrostatic and dispersion dominate the attraction for the optimized stable structure; while for the long distance, it becomes pure electrostatic force. The covalent character was analyzed by the AIM theory, topological analysis on electron density function, delocalization index, and reduced density gradient; and it suggests the very weak strength of hydrogen bond with non-covalent character.