2090 Al-Li alloy electron beam welding joints were heat treated after welding, and the heat treatment scheme was 530 °C quenching for 0.5 h + 190 °C artificial aging for 12 h. Results show that the strength of 2090 Al-Li alloy joint is from 331 MPa in the as-welded state to 415 MPa under the condition of post-weld heat treatment. Therefore, the post-weld heat treatment can increase the strength of Al-Li alloy joints greatly. The observation of joint microstructure demonstrates that the grain morphology of the weldment varies form equiaxed dendrites in as-welded state into equiaxed grains after heat treatment, and the fine strengthening phases precipitate within the grain and along the grain boundary. The XRD analysis of phase constituent indicates that the main strengthening phases in Al-Li weldment are δ′(Al3Li), T1(Al2CuLi) and β′(Al3Zr), etc. The TEM observation shows that after heat treatment, many strengthening phases of spheroidal δ′ and needle-like T1 precipitate in weld metal of 2090 Al-Li alloy joint, which contribute to the joint strength. The observation of joint tensile fracture shows that the Al-Li alloy electron beam welding joint presents the characteristic of transgranular ductile fracture in the as-welded state. After post-weld heat treatment, the Al-Li alloy welded joint presents the pattern of intergranular fracture