The ammonia oxidation reaction (AOR) is a key challenge limiting the performance of direct ammonia anion exchange membrane fuel cells (DA-AEMFCs) due to sluggish kinetics and catalyst poisoning. Herein, we report a metal–support interaction tuning strategy using molybdenum carbide supports to systematically regulate AOR activity of PtIr catalysts. By tuning the carburization degree from metallic Mo to Mo₂C and MoC, the electronic structure and d-band center of PtIr are modulated, which is expected to regulate the adsorption/desorption behavior of reaction intermediates during AOR. The optimized PtIr/Mo₂C catalyst exhibits superior activity (111.6 A g_PGM⁻¹) and high single-cell power density (278.6 mW cm⁻²). This work provides a controllable interfacial engineering strategy for favorable intermediate binding and advancing high-performance AOR electrocatalysis.