<p>Due to its high strength and excellent corrosion resistance, 5A06 aluminum alloy is widely used as a key structural component in the aerospace industry. However, its low plasticity at room temperature makes it prone to excessive thinning and cracking defects during forming, which limits its further application. To solve the above problem, a composite forming method combining a controllable flexible-die and high strain rate was proposed in this study. In this process, the high strain rate is achieved by magnetic pulse loading that drives a piston to impact the MR fluid, while the flexible-die controllability is realized by adjusting the magnetic field to change the rheological properties of the magnetorheological fluid. The deformation behavior of 5A06 aluminum alloy sheet during the high-strain-rate magnetorheological flexible-die forming process was studied through experiments and finite element method (FEM) simulations. The strain rate sensitivity of the 5A06 aluminum alloy sheet was revealed through quasi-static, medium, and high strain rate tensile tests, and a Johnson-Cook constitutive model was established. Results showed that the strength and plasticity of the 5A06 aluminum alloy increase simultaneously at high strain rates in uniaxial tensile deformation. The spatial distribution of magnetic flux density, magnetic pressure, and loading dynamics was systematically studied through electromagnetic field analysis of the magnetic pulse loading system. The mechanical properties and deformation strain rate of the MR fluid have a comprehensive effect on the bulging behavior of 5A06 aluminum alloy sheet under a single magnetic pulse impact. The bulging height significantly increases with the increase of discharge voltage, and slightly decreases with the increase of coil input current. This paper can provide in-depth insights for understanding the deformation behavior of sheet metal in magnetorheological flexible-die forming under high strain rate.</p>