Developing low-cost Cu-based photocatalysts is a promising strategy to boost catalytic activity for nitrogen (N2) photofixation, but it remains a challenge. Herein, we successfully applied porous CuFe to construct plasmon-assisted Cu-based photocatalysts in N2 photofixation via plasmonic catalysis. Surface Fe atoms were regarded as the active sites to efficiently adsorb and activate N2, while Cu frameworks generated hot electrons by surface plasmon resonance (SPR). Impressively, porous Cu96Fe4 attained an NH3 production rate of 342 μmol·gcat.–1·h–1 in N2 photofixation without any sacrificial agents. More importantly, porous Cu96Fe4 also displayed excellent stability by maintaining ∼100% initial activity after 10 cycles. Further mechanistic studies revealed that the valence state and coordination numbers of Fe atoms in porous Cu96Fe4 increased during catalytic process, indicating the formation of a surface nitrogen-containing complex. In addition, the reaction barrier significantly decreased because of the efficient polarization of N2 over Fe atoms.