Fe-based amorphous alloys are widely used in power electronics fields such as transformers and reactors due to their low coercivity, high permeability and low loss. However, the relatively low saturation magnetization (B_s) limits their further applications. Generally speaking, the adjustable magnetic Fe content as an effective strategy can ameliorate the magnetic properties, and the higher the Fe content, the higher the obtained B_s is, but the decrease of the corresponding non-magnetic element content will result in the drop of the ability of alloys to form amorphous phase, leading to the deterioration of the magnetic softness and bending ductility of nanocrystalline alloys. To address this critical issue, in this work, based on the metal-metalloid hybridization, the FePBCCu amorphous ribbons, each with a thickness of ~25 μm, are prepared by the single-roller melt spinning method via 7% (atomic percent) B substitution for P, and the effects of B element addition on the ability to form amorphous phase, magnetic properties and mechanical properties of ribbons are investigated. Thermodynamic behavior shows that the addition of small quantities of B element can reduce the structural heterogeneity of alloy and the crystallization driving force as well, thus effectively improving the thermal stability of the amorphous matrix. The melting and solidification curves show that the addition of B can promote alloy to approach to the eutectic composition, and there is a large degree of undercooling. As a result, the critical thickness of ribbons increases from ~21 μm for B-free alloy to ~30 μm for B-added alloy due to the micro-alloying effect. The addition of B increases the effective magnetic moment of magnetic atoms in alloy, resulting in the increase of the saturation magnetization. Furthermore, the results of nanoindentation tests show that the modulus value of the B-added alloy decreases greatlyr and fluctuates in a smaller range than that of the B-free alloy, which is closely associated with the structural uniformity of the alloy.