The effect and mechanism of Fe element addition in Cu36Zr48Ag8Al8 BMG on structure and mechanical properties were investigated. Effects of phase separation structure and nanocrystalline precipitation on mechanical behaviors were analyzed. Vickers hardness tests were used to study the effect of Fe addition on the hardness and shear band features of the BMG. The results show that Fe-enriched and Cu, Ag-enriched amorphous phase are light and dark phase in TEM contrast, respectively. Phase separation structure with different modulus and hardness in the amorphous alloy, leads to strain hardening behavior under loading. And the nanocrystallines smaller than 5 nm form and dispersion further strengthens the amorphous matrix. A few semi-circular shear bands form around Vickers indention of the amorphous phase. And more semi-circular shear bands with a smaller distance form as the indenter presses on the structure with better plasticity. The Vickers hardness of crystalline phase is lower than that of the amorphous phase, and no flaw exist around the indention