Abstract: With the continuous increase in municipal solid waste incineration fly ash production, its resource utilization has become increasingly urgent. This study investigated the leaching of valuable metals from fly ash using an oxalic acid-sulfuric acid composite system. The effects of oxalic acid concentration, liquid-to-solid ratio, volume ratio of oxalic acid to sulfuric acid, leaching temperature, and time on the extraction rates of Al, Zn, Cu, and Fe were systematically examined. The results showed that under the optimized conditions（0.8 mol/L oxalic acid, a liquid-to-solid ratio of 15 mL/g, an oxalic to sulfuric acid volume ratio of 9∶6, a temperature of 80 ℃, and a time of 90 min）, the leaching rates of Al, Zn, and Fe all exceeded 98%, while that of Cu was over 93%. The composite system not only provided sufficient H⁺ but also selectively complexed target heavy metals. Oxalic acid, with its excellent complexation and reductive dissolution capabilities, formed soluble complexes with metal ions. The synergistic effect of the combined acids effectively enhanced metal leaching. The leaching kinetics were fitted using the unreacted shrinking core model. The apparent activation energies for Al, Zn, Cu, and Fe, calculated via the Arrhenius equation, ranged from 17.83 to 21.40 kJ/mol, indicating that the leaching process was likely governed by a mixed mechanism involving both surface reaction and diffusion control.