Eutectic high-entropy alloys exhibit high strength and excellent ductility, and their properties are determined by their microstructure. Magnetic fields, as extreme external physical fields, have been widely proven to significantly affect the solidification process of alloys. Therefore, research on the theory of metallic solidification under a high magnetic field is highly important. The effect of a magnetic field on the directional solidified AlCoCrFeNi2.1 eutectic high-entropy alloy under different drawing speeds was studied. The microstructures of the AlCoCrFeNi2.1 eutectic high-entropy alloy under magnetic field-assisted directional solidification include primary phase dendrites (FCC phase) and eutectic lamellar phases (FCC/BCC phase). The strong magnetic field improves the hardness and tensile properties by enhancing the stability of the solid-liquid interface, refining the spacing of the eutectic lamellar layers and changing the preferred orientation of the primary phase. Under a high magnetic field, the elongation of the AlCoCrFeNi2.1 eutectic high-entropy alloy reaches approximately 33%, with an ultimate tensile strength of 985 MPa. Therefore, a strong magnetic field can be used as an effective way to obtain the coupling of strength and toughness during the casting process.