The invention discloses an electron beam welding method for a dissimilar aluminum alloy material, and belongs to the technical field of welding. The method comprises the steps that 1, a welded joint is designed, wherein the welded joint adopts a lock bottom butt joint form; 2, a workpiece to be welded is formed by assembly; 3, the workpiece to be welded is placed in a vacuum chamber, and vacuumizing is carried out; 4, the track of a welded seam is subjected to teaching; 5, positioned welding is carried out on the workpiece to be welded; 6, formal welding is carried out on the workpiece to be welded, wherein the welding parameters meet the conditions that the working distance is 200mm, the acceleration voltage is 50kV, the focusing current of the surface focus is -(0.01-0.03)A, the electron beam current is 50-70mA, and the welding speed is 900-1100mm/s; and 7, modification welding is carried out on the welded seam, wherein the welding parameters meet the conditions that the working distance is 200mm, the acceleration voltage is 50kV, the focusing current of the surface focus is +(0.05-0.1)A, the electron beam current is 30-40mA. According to the method, the quality of the welded seam can be improved, and the defect of the welded seam can be reduced.