Abstract: Objective The aim is to solve the problems of insufficient temperature control accuracy and unstable weld quality in the brazing process of semi-circular tubes of airconditioner condenser and evaporator. Methods In this study, an innovative automatic flame brazing technology with multi-stage temperature gradient and composite heat source synergy was proposed. The technology enabled precise control of brazing thermal process through a four-stage temperature control system (preheating, brazing, insulation, and nitrogen cooling) and a differentiated heat source configuration (oxygen-natural gas high heat source combined with air-natural gas temperate heat source). Results The batch verification of 20 000 sets of modules shows that the technology improves temperature control accuracy to ±5 ℃ (the original process ±25 ℃), welding leakage rate is reduced from 38×10⁻⁴ to 8×10⁻⁴. Conclusion The research effectively solves the problems of uneven distribution of brazing filler metal, coarse grain of base metal and post-welding oxidation caused by traditional processes, and provides a high-stability and high-quality connection solution for the manufacture of airconditioner heat exchanger, which has important engineering application value.