Heat exchanger, comprising: a first sub-heat exchanger (100, 500) having a first manifold (110, 510), a second manifold (120, 520), and at least two heat exchange tubes which extend between the first manifold (110, 510) and the second manifold (120, 520) and are in fluid communication with the first manifold and the second manifold; and a second sub-heat exchanger (200, 600) having a third manifold (210, 610), a fourth manifold (220, 620), and at least one heat exchange tube which extends between the third manifold (210, 610) and the fourth manifold (220, 620) and is in fluid communication with the third manifold (210, 610) and the fourth manifold (220, 620), wherein at least one of the heat exchange tubes in the first sub-heat exchanger (100, 500) is part of a flow path of the second sub-heat exchanger (200, 600), wherein the first sub-heat exchanger (100, 500) comprises a first heat exchange region and a second heat exchange region, wherein the first heat exchange region and the second heat exchange region are spaced apart by a first partition disposed in the first manifold (110, 510) and are distributed in a longitudinal direction of the manifold (110, 510), the first sub-heat exchanger (100, 500) comprises a first inlet (112, 512), a second inlet (122, 522), and a first outlet (114, 514), and the second sub-heat exchanger (200, 600) comprises a third inlet (211, 611) and a second outlet (212, 612), wherein the first inlet (112, 512) is located in the first heat exchange region, and the second inlet (122, 522) and the first outlet (114, 514) are located in the second heat exchange region, the second outlet (212, 612) is in fluid communication with the second inlet (122, 522), and the first heat exchange region and the second heat exchange region are in fluid communication by means of the second manifold (120, 520), characterized in that the first sub-heat exchanger (100, 500) further comprises a third heat exchange region, wherein the third heat exchange region is spaced apart from the first heat exchange region and the second heat exchange region by a third partition in the first manifold (110, 510) and a fourth partition in the second manifold (120, 520), a fourth inlet (111, 511) and a fourth outlet are provided in the third heat exchange region, and the fourth outlet is in fluid communication with the third inlet (211, 611). a first sub-heat exchanger (100, 500) having a first manifold (110, 510), a second manifold (120, 520), and at least two heat exchange tubes which extend between the first manifold (110, 510) and the second manifold (120, 520) and are in fluid communication with the first manifold and the second manifold; and a second sub-heat exchanger (200, 600) having a third manifold (210, 610), a fourth manifold (220, 620), and at least one heat exchange tube which extends between the third manifold (210, 610) and the fourth manifold (220, 620) and is in fluid communication with the third manifold (210, 610) and the fourth manifold (220, 620), wherein at least one of the heat exchange tubes in the first sub-heat exchanger (100, 500) is part of a flow path of the second sub-heat exchanger (200, 600), wherein the first sub-heat exchanger (100, 500) comprises a first heat exchange region and a second heat exchange region, wherein the first heat exchange region and the second heat exchange region are spaced apart by a first partition disposed in the first manifold (110, 510) and are distributed in a longitudinal direction of the manifold (110, 510), the first sub-heat exchanger (100, 500) comprises a first inlet (112, 512), a second inlet (122, 522), and a first outlet (114, 514), and the second sub-heat exchanger (200, 600) comprises a third inlet (211, 611) and a second outlet (212, 612), wherein the first inlet (112, 512) is located in the first heat exchange region, and the second inlet (122, 522) and the first outlet (114, 514) are located in the second heat exchange region, the second outlet (212, 612) is in fluid communication with the second inlet (122, 522), and the first heat exchange region and the second heat exchange region are in fluid communication by means of the second manifold (120, 520), characterized in that the first sub-heat exchanger (100, 500) further comprises a third heat exchange region, wherein the third heat exchange region is spaced apart from the first heat exchange region and the second heat exchange region by a third partition in the first manifold (110, 510) and a fourth partition in the second manifold (120, 520), a fourth inlet (111, 511) and a fourth outlet are provided in the third heat exchange region, and the fourth outlet is in fluid communication with the third inlet (211, 611).