The invention relates to the technical field of welding, and discloses a friction welding method of a target material assembly, according to the friction welding method, heat generated by friction between a target material rotating at a high speed and a back plate is used for locally melting a first boss and a second boss, and a compact solid-phase welding seam is formed under extrusion of a welding tool. According to the friction welding method, the welding bonding layer is formed through melting, the bonding strength is higher than that of brazing indium, the high-temperature resistance is better, and desoldering is not prone to occurring; compared with electron beam welding, the welding area of the first boss and the second boss is larger, namely, the metallurgical bonding area is larger, and the overall strength is higher; compared with diffusion welding, the friction welding method is shorter in consumed time, inert gas or other working conditions do not need to be adopted for protection, and the cost is low; and secondly, the friction welding method is small in friction force, low in equipment requirement, low in energy consumption and short in welding time consumption, and small-area contact friction is not prone to causing overall deformation of the target material or the back plate.