Abstract: A heat exchanger is provided, including a heat exchanger core. The heat exchanger core at least includes a first core part, a second core part and a third core part which are stacked. The first core part, the second core part and the third core part are formed by stacking plates. The third core part is located between the first core part and the second core part. The first core part is in the form of unilateral flow. The second core part is in the form of diagonal flow. The third core part can realize transformation of flow channel forms of the first core part and the second core part, and is stacked with the first core part and the second core part, and thus the heat exchange efficiency is good.