Combustion experiments were performed for polyethylene (PE) in stagnation-point flow to investigate the fundamental characteristics of PE in high-temperature air combustion (HiTAC). Air diluted by nitrogen, water vapor, and carbon dioxide was tested as the oxidizer, and the oxidizer temperature was varied from 300 K to 773 K in order to investigate the effect of the dilution and temperature on the regression rate, the extinction limit, and the sooting limit of PE. The kinetic parameters of PE pyrolysis under the combustion conditions were estimated from the regression rate experimental data using a new method that combines experiments and numerical simulations. It was found that the previously reported kinetic parameters obtained with thermal gravimetric analysis (TGA) were much smaller than those obtained in this study. It was also found that the kinetic parameters varied when a different dilution gas was used, indicating that PE pyrolysis is affected by the composition of oxidizer.