The utility model discloses a preheating device for cold start of an engine, which is low in cost, is small in volume and size, is efficient and energy-saving, and is convenient for large-range popularization and utilization. An air exhausting pipe (2) of the engine (1) is connected with a heat storage heat exchanger (3) in parallel; the heat storage heat exchanger (3) is used for storing air exhausting residual heat of the engine (1); the heat storage heat exchanger (3) is of a columnar structure and is internally provided with a plurality of heat storage units; each heat storage unit is a concentric sleeve (7) comprising inner and outer pipes; a phase-change heat storage material (8) is packaged in an annular space between the inner and outer pipes; the two ends of the inner pipe are respectively welded on two flow guide discs (9); and a cavity for the passing of cooling water of the engine (1) is commonly formed by the two flow guide discs (9), and an inner wall of the heat storage heat exchanger (3) between the two flow guide discs (9).