The work aims to prepare thick oxidation resistance Cr coating with high-temperature accident tolerance on Zr-4 fuel claddings (ATF), so as to protect Zr substrate from exposure to high temperature steam vapor. A 20 μm Cr was prepared by a home-made φ155 mm large arc-source on Zr-4 alloy substrate (>3 μm/h). Phase composition before and after oxidation was analyzed by X-ray diffraction (XRD) and defects generated at different temperature were analyzed by scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA) to investigate the protective mechanism of Cr coating to Zr substrate. When deposition rate was >3 μm/h, the Cr coating was uniform and dense with excellent resultant force and columnar crystal structure and could withstand at least 15.8% of plastic deformation and had better plastic deformation ability. After coated samples were oxidized at 1000 °C, 1100 ℃, and 1200 ℃ for 1 h and cooled in air down to room temperature (RT), the thick Cr coating turned into four sublayers to protect the Zr-4 substrate: outer CrOx layer, inner Cr2O3 layer, residual Cr layer, and Cr-Zr diffusion layer. Even after the toughest test (1200 ℃/3600 s), except the outer oxide layer remaining continuous adhesion to the Zr-4 alloy, a 6.8 μm residual Cr layer still existed on the substrate. Twice oxide ruptures were formed to prevent the further damage. The Cr-Zr diffusion layer was formed by Zr element permeating to the Cr coating. The formation of sub-surface voids were clearly related to brittle α-Zr(O) turned by β-Zr(O) and Sn/Cr segregations near the surface. Zr-O channels formed by columnar crystal structure of residual Cr layer were the key factors of coatings failure. The ~20 μm Cr coating cladded on Zr alloy has sufficient accident tolerance. Zr-4 alloy substrate is not exposed under severe accident condition for all flaws. The thick Cr coating can create effective barriers to prevent the zirconium alloy substrate from causing nuclear accident and avoid further damage to the substrate.