The invention discloses a radiation device, which comprises a flat heat pipe and overlapped radiation fins, wherein each radiation fin is provided with a rectangular accommodating hole for accommodating the condensation section of the flat heat pipe and at least one solder paste feeding hole communicated with the accommodating hole and used for accommodating solder paste, a connecting wall is extended from the edge of the accommodating hole in each radiation fin and comprises a longitudinal upper flat plate, and a longitudinal lower flat plate and a short edge which are opposite to the longitudinal upper flat plate, and the short edge extends toward the upper flat plate from one end of the lower flat plate; the solder paste feeding holes are formed at the intersection of the upper flat plates and the short edges; the condensation section of the flat heat pipe is inserted in the accommodating holes in the radiation fins and keeps a clearance with the connecting walls of the radiation fins; and the solder paste fed from the solder paste feeding holes, after being melted, fills up the clearance for fusing the flat heat pipe and the radiation fins together. The solder paste feeding holes are formed on one lateral side of the accommodating holes; and after welding, the effective contact face of the flat het pipe is in complete contact with the connecting walls of the radiation fins.