Abstract: Objective The purpose was to explore microstructure of weld and mechanical properties of 55 mm large thickness 2219 aluminum alloy electron beam welded joints at different thickness positions, and provide a basis for further process optimization and engineering practice. Methods Microstructure and mechanical properties of welded joints were studied through metallographic test tensile test, bending test and microhardness test. Results The results showed that electron beam welded joints were well formed, depth-to-width ratio reached 18.3～18.5. Microstructure of weld was not very different in the thickness direction, showing good consistency. Weld was fine equiaxed structure, difference of microstructure in weld thickness direction was small, and stirring of scanning function played the role of refining grains of weld. Tensile performance, bending performance and microhardness of weld in the thickness direction showed good consistency. Tensile strength of weld reached 95% of base material and the maximum difference in thickness direction was 7 MPa. Bending performance was good and bending angle reached 180°. Microhardness was stable at 50～60 HV0.1. Conclusion Electron beam welded joints of large thickness 2219 aluminum alloy had good microstructure uniformity and comprehensive mechanical properties in thickness direction.