Big-data analysis of phase-formation rules of high-entropy alloys (HEAs) was conducted and a phase for-mation rule from a dynamic view was deduced.It was indicated in literatures that cooling rate has a strong influence on the phase formation of HEAs.Higher cooling rate may promote the generation of amorphous phase, and accordingly suppress the formation of intermetallics.Meanwhile, it was also shown that cool-ing rate had little impact on the formation of solid-solution phase.To demonstrate this rule, a series of Fe-CoNi(AlSiB)x HEAs ribbons were fabricated by a melt-spinning technique, and the microstructure, me-chanical, and magnetic properties were also investigated.The results show that all ribbons exhibit disor-dered solid-solution structure.The addition of boron changes the alloy from ductility to brittleness, but without evident change of magnetic properties.The alloy in the nominal composition of FeCoNi(AlSi)0.2 has the best combination of mechanical and magnetic properties.A distinct feature of HEAs in magnetiza-tion was noticed and explained.