Fe-based bulk metallic glasses (BMGs) typically exhibit ultrahigh strength but a poor ductility. Here, an Fe₆₂Ni₁₈P₁₃C₇ BMG with a super large plasticity of above 50% is reported. Such a discovery is guided by understanding a composition-strength-ductility map, in which most of Fe-based BMGs are classified into three types: FeC(B)-based, FeB-based, and FeP(C)-based. We demonstrate that the mechanical properties of the different types of BMGs are linked with their different physical properties. Among the three types of BMGs, the FeP(C)-based BMGs often possess a lower glass transition temperature, a lower shear modulus, and a higher Poisson's ratio, resulting in a lower shear flow barrier and a higher plasticity. Our findings provide a guideline in understanding the mechanical behavior of Fe-based BMGs.