Disclosed are a fuel cladding and a fuel assembly, wherein the fuel cladding comprises a zirconium alloy substrate, an intermediate layer arranged on the zirconium alloy substrate and having non-stoichiometry and gradient characteristics, and an ambient shielding layer arranged on the intermediate layer; and the intermediate layer and the ambient shielding layer form a gradient multiphase coating having non-stoichiometry on the zirconium alloy substrate. The fuel cladding overcomes the problems in a single coating of conventional zirconium alloy claddings, such as interfacial stresses, interfacial diffusion and zero tolerance to high temperature vapour oxidation, is applicable to accident fault-tolerant nuclear fuel cladding uses, and greatly improves the anti-accident ability of a nuclear reactor to maintain nuclear fuel assembly structure and functional integrality under severe accident conditions, and a safety threshold thereof.