Ammonia plays a vital role in the development of modern agriculture and industry. Compared to the conventional Haber–Bosch ammonia synthesis in industry, electrocatalytic nitrogen reduction reaction (NRR) is considered as a promising and environmental friendly strategy to synthesize ammonia. Here, inspired by biological nitrogenase, we designed iron doped tin oxide (Fe-doped SnO₂) for nitrogen reduction. In this work, iron can optimize the interface electron transfer and improve the poor conductivity of the pure SnO₂, meanwhile, the synergistic effect between iron and Sn ions improves the catalyst activity. In the electrocatalytic NRR test, Fe-doped SnO₂ exhibits a NH₃ yield of 28.45 μg·h⁻¹·mg_cat⁻¹, which is 2.1 times that of pure SnO₂, and Faradaic efficiency of 6.54% at −0.8 V vs. RHE in 0.1 M Na₂SO₄. It also shows good stability during a 12-h long-term stability test. Density functional theory calculations show that doped Fe atoms in SnO₂ enhance catalysis performance of some Sn sites by strengthening N–Sn interaction and lowering the energy barrier of the rate-limiting step of NRR. The transient photovoltage test reveals that electrons in the low-frequency region are the key to determining the electron transfer ability of Fe-doped SnO₂.