The pyro-hydrolysis method is a crucial way to treat calcium chloride (CaCl₂)-containing solid waste to achieve environmental friendliness and efficient utilization. In this paper, we have conducted both DFT (density functionary theory calculation) calculations and experiments by flowing carbon dioxide (CO₂) and steam (H₂O) on the CaCl₂ in a fluidized bed. The thermogravimetric analysis reveals that the pro-hydrolysis reaction can proceed more vigorously at temperatures ranging from 300 to 500 °C. The structure characterization of residues collected from the pyro-hydrolysis of CaCl₂ was characterized using X-ray diffraction (XRD), X-ray Photoelectron Spectrometer (XPS), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The XRD patterns show that a small amount of CaCl₂ was decomposed into calcium chloride hydroxide (Ca(OH)Cl) in a fluidized bed with O₂ at temperatures above 450 °C. Nevertheless, with the presence of CO_2, CaCl₂ can convert into calcium carbonate (CaCO₃) at a lower temperature. The SEM-EDS displays a swelling structure that appears on the CaCl₂ particles surface after the thermal decomposition with CO₂, and the content of Cl element at a specific position is significantly reduced. DFT calculations is shown that when CO₂ and H₂O are bonded to form a carbonic acid complex adsorbed on the surface, the energy barrier for the rupture of the H-OH bond and Ca-Cl bond is dramatically decreased, and the dissociated H⁺ combined with the Cl^- to form hydrogen chloride (HCl). The overall reaction pathway only adsorbs 1.099 eV energy. This research is useful for promoting knowledge of the chlorine evolution mechanism for pyro-hydrolysis of CaCl₂ in CO₂ atmosphere.