The liquid phase diffusion bonding between CuW alloy and 20 steel was studied. The brittle Fe2W intermetallic compound thin layer was formed at the interface of CuW near the transition layer of the monolithic material, which seriously deteriorated the mechanical properties of the joint. The CuW/20 steel monolithic material containing copper chromium interlayer was prepared in the range of 1200 ℃~1380 ℃. After the interlayer was added, a complete metallurgical transition layer was formed at the interface between CuW alloy and 20 steel, eliminating the thin layer of Fe2W brittle intermetallic compound produced in the process of direct diffusion bonding. It was observed under the optical microscope that the interface transition layer was composed of dark worm like structure surrounded by a light colored matrix. The results of XRD and EDS analysis showed that, The light colored matrix is divided into copper phase and the black vermicular structure is rich in iron phase. With the increase of diffusion bonding temperature, the dark worm like structure in the interface transition layer extends from one side of 20 steel to the copper matrix and grows continuously. When diffusion bonding at 1250 ℃, dark wormlike tissue is evenly distributed in the entire transition layer. The mechanical properties of CuW/20 steel composites at different temperatures were tested at room temperature. It was found that the interface strength reached the maximum of 145Mpa at 1250 ℃. The tensile fracture morphology was observed by SEM, and it was found that the overall interface was flat without dimples, consisting of Cu phase ductile tear edges and flat iron rich phase area.