The modulation mechanism of iron (Fe) and manganese (Mn) in transition‐metal elements on the interface bonding and mechanical properties of bronze (Cu3Sn)‐based/diamond composites is investigated through first‐principles calculations. Transition‐elements‐doping scenarios are investigated employing six‐layer slab models. It is revealed that the doping of Fe or Mn can make the Cu3Sn/diamond interface more stable, which effectively improves the wettability of the Cu3Sn/diamond interface based on the calculation results and analysis of interface energy, differential charge density model, and density of states. However, co‐doping with both Fe and Mn weakens the wettability of the Cu3Sn/diamond interface. Finally, wettability tests and microstructure characterizations demonstrate that the doping of Fe and Mn represents an effective approach to controlling the interface bonding performance of bronze/diamond composites.