In recent years, due to the unique design concept and excellent mechanical and physical, and chemical properties, studies on medium- and high-entropy alloys have become a research hotspot in the field of high-performance metal materials. However, high strength and large plasticity are simultaneously achieved by adopting cold/hot processing treatments together with reasonable heat treatmentsfor most medium- and high-entropy alloys. To rapidly strengthen the medium- and high-entropy alloy, the Fe49.3Co23Ni23C0.85Mn1Si2.85 medium-entropy alloys with different gradient structure features were obtained using the vacuum electron beam selective melting technique. Under the same scanning mode and scanning time, the thickness of the remelted layer increases with the increase of electron beam current. The mechanical test results show that the best combination of properties together with relatively refined grains was obtained when the electron beam current is 15 mA. Moreover, the corresponding average thickness of the remelted layer is 240 μm, the surface hardness is 213 HV, the tensile strength is increased to 823 MPa, and the elongation is maintained to be 59% . The experimental results show that the mechanical properties of medium- and high-entropy alloys can be effectively strengthened by the rapid vacuum electron beam surface melting technology.