The electron beam welding process was used to weld the dissimilar metals of 7075 aluminum alloy and TC4 titanium alloy.The morphological characteristics,formation reasons and control measures of welding defects were studied. The results show that defects such as pores,cracks and shrinkage cavities occur in the electron beam welding head of dissimilar metals in aluminum alloy and titanium alloy. Adjusting the welding process parameters and changing the relative energy distribution of the beam spot on the dissimilar base material can eliminate defects such as pores and cracks. At the same time,the metal cooling time of the weld metal is prolonged,so that the liquid molten pool can replenish the pores generated during the solidification process,and the surface focus is used to reduce the volume of the molten pool,and the shrinkage cavity in the weld seam is improved. The best welding parameters are: working distance 272 mm,electron beam current 18 mA,welding speed 20 mm/s,focusing current 415 mA. The test provides a reference for improving the quality of aluminum alloy titanium alloy dissimilar metal electron beam welded joints.