The effects of welding current, welding speed, welding direction & welding torch angle and steel side groove angle on the weld formation of Q890D steel/6061 aluminum alloy were studied, and the effects of welding current and welding speed on the interface structure and mechanical properties of Q890D steel/6061 aluminum alloy MIG welding joint were analyzed under optimized welding process. The results show that the suitable welding direction of Q890D steel/6061 aluminum alloy is right welding method, the suitable angle of welding torch is 10°, the suitable angle of steel side groove is 45°, and the welding wire position should be in the middle of the steel side groove, the suitable welding current and welding speed are 105 A and 50 cm/min respectively; the fracture position of MIG welding joint of Q890D steel/6061 aluminum alloy with different welding current and welding speed is in the interface zone; in MIG welding process, the doublelayer intermetallic compound layer structure of(Fe,Cu)2Al5near the steel side and (Fe, Cu)4Al13near the aluminium side formed in the interfacial zone is helpful to improve the welding quality.