Abstract: High strength Al-Li alloy was brazed in furnace by using Ag-Al-Cu-Zn filler metal with CsF-AlF3 flux. The results show that under the condition of N 2 atmosphere, the tensile strength of butt joint is up to about 390 MPa with the strength factor of 0.89 and the shear strength of lap joint is up to about 380 MPa with the strength factor of 0.86, which all the strength factors are higher than those of fusion welding and brazed joints of high strength Al-Li alloy reported.The experimental results and theoretical analyses show that, effectively destroying and removing the complex oxide films on the surface of Al-Li alloy under the temperature of about 530℃ is the key factor to the brazing process and the protection of N₂ is an important way to improve mechanical properties of the braze metal.