Abstract: With the advantages of both Cu and Al, including high conductivity, good corrosion resistance, low density, and easy connectivity, Cu–Al-laminated composites become a substitute for copper plates which can be applied widely in the fields of telecommunication, the petrochemical industry, transportation, decorative buildings, and the aerospace, national defense, and military industries. Cu–Al-laminated composites can be prepared via various methods, such as the explosive combined method, rolling combined method, and cast-rolling combined method. However, all these methods are limited because of the complicated metal surface treatment which poses a restriction on the development of this kind of plate. To resolve this issue, a new process of horizontal continuous casting composite forming (HCCF) for bimetal composite plates with an interface of metallurgical bonding, which is regarded as a short and more efficient process, was presented in this paper. Cu–Al composite plates with a section size of 70 mm × 24 mm (width × thickness) were fabricated, whose feasible preparation parameters were further studied, along with the investigation of the microstructure and properties of the composite plate. The results show that consisting of intermetallic compounds and eutectic phase, an interfacial layer is formed during the preparation and formation of the Cu–Al composite plate. Layer II of θ is formed via a solid–liquid transition during the solidification of liquid Al on the solid Cu plate. With the Cu atoms continuously diffusing into the Al liquid, layer I of γ is formed via a solid–solid transition with a certain content of Cu atoms, while layer III of α + θ is formed via eutectic transformation under the eutectic temperature. Making of Cu–Al intermetallic compounds, Layer I and layer II are the main areas of crack generation and expansion, thus, the thickness of the interface layer plays an important role that can control bonding strength. The temperature distribution of the composite Cu–Al plate during solidification is optimized by adjusting the parameters and controlling the formation of the composite layer. Therefore, a reasonable matching of the process parameters is the key to improving the microstructure of the composite layer and increasing the bond strength of the clad plate.