The utility model discloses a double-pipe heat exchanger. Including an inner tube, two ends of the inner pipe are respectively used as a cooling medium inlet and a cooling medium outlet; the inner pipe is arranged in a winding manner; the inner pipe comprises at least two straight pipe sections and at least one bent pipe section for connecting the at least two straight pipe sections; each straightpipe section is sleeved with an outer pipe; each outer pipe comprises an inlet end and an outlet end; every two adjacent outer pipes are communicated with each other through a connecting pipe; the connecting pipe is connected between the outlet end of one of the two adjacent outer pipes and the inlet end of the other one of the two adjacent outer pipes; and one of the outer pipe sleeved on the straight pipe section provided with the cooling medium inlet and the outer pipe sleeved on the straight pipe section provided with the cooling medium outlet is provided with a to-be-cooled medium inlet,and the other one is provided with a to-be-cooled medium outlet. The inner pipe and the outer pipe of the double-pipe heat exchanger are easy to install, and the overall structure is stable and firm.