Being in use for fixing a radiator on circuit board, the fixing device includes a backboard and a buckle tool. The buckle tool includes a bunt press portion and two buckle pins extended from two endsof the bunt press portion, and buckle join portion is formed on each buckle pin. The backboard includes a main body and buckle ears, which are matched to the buckle join portion of the buckle tool, setup on the main body. A connecting portion of backboard is setup and penetrated at upside of circuit board. Being matched to the buckle tool, the fixing device installs radiator on circuit board firmly without need of using the fixed base setup on circuit board to match to backboard or the buckle join piece like current technique needs to. Features are: simple structure, easy of production, savingmaterial and cost.