The copper-clad aluminum (CCA) composite wire combines the excellent electrical conductivity of copper and the light weight of aluminum, and replacing the copper-core wire can effectively reduce the weight of cable network. This paper adopts the methods of assembly performance test, metallographic inspection, FIB and SEM in-situ inspection, to analyze the reasons for the failure of CCA assembly after environment test. When the sealing of the assembly is not good, the crimping position of the CCA wire communicates with outside by forming an air leakage channel, which will cause corrosion of the aluminum core and lead to the failure of the assembly. By improving the strain matching of the materials at crimping position and insuring the integrity of sealing structure, the sealing crimping can be achieved, effectively improving the reliability of CCA assembly.