The invention provides a heat exchanger. The heat exchanger comprises a tube pass side and a shell pass side, wherein the tube pass side comprises an inlet tube, an inlet cavity, a heat transfer tube bundle, an outlet cavity and an outlet tube; hot fluid enters the inlet cavity from the inlet tube and sequentially passes through the heat transfer tube bundle, the outlet cavity and the outlet tube; the shell pass side comprises an inlet channel, an inner shell, an outer shell and an outlet cavity; cold fluid sequentially passes through the space defined by the inlet channel, the inner shell and the outer shell, and the outlet cavity; the inlet cavity, the heat transfer tube bundle and the outlet cavity are arranged in the space defined by the inner shell and the outer shell; the inner shell and the outer shell are arc-shaped; the heat transfer tube bundle is arc-shaped; and the arc shape of the heat transfer tube bundle and the arc shapes of the inner shell and the outer shell have the same center of a circle. The heat exchanger has the beneficial effects that the heat transfer tube bundle of the heat exchanger is of an arc-shaped structure, the heat transfer tube bundle, the inner shell and the outer shell have the same arc-shaped structure, and the heat transfer tube bundle can freely expand with heat and contract with cold in the space defined by the inner shell and the outer shell, so that the heat transfer tube bundle is applicable in relatively wide temperature range and fluid range, and the application range of the heat exchanger is greatly expanded.