The deposition of copper layers on polyimide films by magnetron sputtering is widely used in the preparation of flexible copper-clad laminates. At present， low bonding strength between the surface copper film and the polyimide substrate is one of the main problems faced by the magnetron sputtering method in the preparation of flexible copper-clad laminates. This paper proposes to improve the adhesion of copper film on the surface by plasma etching treatment of polyimide substrate and introducing a metal Cr bonding layer. It also compares and studies the effects of different plasma etching and metal Cr layers on the microstructure， density， resistivity， and adhesion of the surface copper film. The results show that plasma etching increases the surface roughness and surface energy of polyimide， which is beneficial for copper film deposition and forms mechanical interlocking and chemical bonds at the interface to improve adhesion. The Cr metal intermediate layer can form a solid solution at the film interface to strengthen the adhesion， reaching the optimal 5B level. This study is of great significance in solving the problem of poor adhesion between copper film and polyimide substrate in the preparation of flexible copper-clad laminates by magnetron sputtering.