To address the corrosion protection issues for hot components of high-end equipment in extreme service environments, the C276 alloy coating was deposited on the surface of 304 stainless steel via high-velocity air fuel (HVAF) spraying. The extreme conditions of 1000 °C temperature, an atmosphere containing 6% HCl, and a flow rate of 30 m/s were simulated in the study using a high-temperature airflow corrosion erosion device. The C276 coating and the 304 stainless steel substrates were subjected to a corrosion test for 25 min. The surface phase composition, element distribution, corrosion product characteristics, and cross-section structure of the samples before and after corrosion were systematically analyzed by means of a scanning electron microscope, an energy dispersive spectrometer, and an X-ray diffractometer. The mechanism of high-temperature chlorination corrosion was deduced through thermodynamic and kinetic analysis. The results show that compared with 304 stainless steel, the C276 alloy coating exhibits better corrosion resistance in an extremely high-temperature environment containing HCl, and the average weight gain and growth rate of the corrosion layer were lower. The main corrosion products on the C276 coating surface are Fe₂O₃, FeO, FeCl₂, NiO, and Cr₂O₃, among which the oxides of Ni and Cr form a continuous and dense protective oxide layer that effectively inhibits the intrusion of corrosive media. The high-temperature HCl corrosion follows the ‘chlorination–oxidation’ cycle mechanism, and Cl₂ plays a catalytic role in the reaction and accelerates the corrosion process.