Abstract: To investigate the combustion characteristics of the cutting flame in external-mixing flame nozzles, this study employed a combined approach of numerical simulation and experimental methods while maintaining consistent characteristics of the cutting oxygen flow field. A systematic analysis was conducted on the influence of preheat oxygen and propane gas pressure on the combustion properties of the cutting flame in external-mixing nozzles. The results indicate that the temperature distribution in the external flow field of the cutting flame ranges from 1700K to 2800K, with high-temperature zones predominantly concentrated in the peripheral regions of the flame, while the temperature along the axis of the cutting oxygen remains relatively lower. Simulation analysis of the combustion characteristics under varying preheat oxygen inlet pressures revealed that at a preheat oxygen inlet pressure of 0.2MPa, the cutting flame exhibits greater length, higher velocity, and more complete combustion. Under a preheat fuel gas inlet pressure of 0.03MPa, the cutting flame achieves optimal length, elevated temperature of the preheat flame, and enhanced envelopment effect. Under these conditions, the cutting oxygen flow velocity at the nozzle outlet approximates 500m/s, and the effective action length of high-purity (≥95%) cutting oxygen along the nozzle axis remains consistently within the range of 250-260mm. At this position, the mass fraction of C₃H₈ decreases abruptly, while the mass fractions of combustion products CO₂ and H₂O increase sharply, indicating the initiation of combustion reactions involving the cutting oxygen. Comprehensive evaluation of the cutting flame combustion characteristics aligns with the rated cutting thickness. This research holds significant theoretical importance and engineering application value for optimizing cutting processes and improving nozzle structures.