In this paper, the effect of a high-temperature oxidizer at different oxygen concentrations on chemical flame length and volume has been numerically studied. Liquified propane gas (LPG) was used as the fuel. Hot exhaust flue gas was used as the dilution gas. The studied parameters include oxygen concentration and temperature of the oxidizer, fuel temperature, fuel firing rate, and diameter of the fuel nozzle. The following results were obtained: (1) Chemical flame length increased as either the oxygen content decreased, the oxidizer temperature increased, or the fuel temperature decreased; furthermore, the chemical flame length was independent of the fuel flow rate and the diameter of the fuel nozzle for the studied cases. (2) Chemical flame volume increased either as the oxygen content decreased and the oxidizer temperature increased, the fuel temperature was reduced, or the fuel firing rate was increased; chemical flame volume was dependent very much on the oxygen concentration in the oxidizer. (3) Influences of high temperature and low oxygen concentration in the oxidizer on the flame Froude number (Fr-f) were examined; regimes of momentum control or buoyancy control were determined on the assumption that the oxidizer temperature and oxygen concentration are changeable. (4) A simple correlation of the chemical flame length and volume, relative to the flow parameters, has been derived in terms of a Frf number for momentum-buoyancy transition jet flame under the high-temperature air combustion (HiTAC) condition. The criteria constants of the dimensionless chemical flame volume (V-*) and the dimensionless chemical flame length (L-*), to assess the momentum- or buoyancy-controlled flame, are given.