A plate heat exchanger, comprising a heat exchange core, and a first flow passage and a second flow passage isolated from each other being formed in the heat exchange core, wherein the heat exchange core comprises first plates and second plates, each of the first plates comprises a front surface and a back surface at an opposite side of the front surface, and each of the second plates comprises a front surface and a back surface at an opposite side of the front surface; portions of the second flow passage are formed between the front surfaces of the first plates and the back surfaces of the adjacent second plates, and portions of the first flow passage are formed between the front surfaces of the second plates and the back surfaces of the adjacent first plates; the first plate comprises a first corner hole, a second corner hole, a third corner hole and a fourth corner hole, and the second plate also comprises a first corner hole, a second corner hole, a third corner hole and a fourth corner hole; the first corner hole, the second corner hole, the third corner hole and the fourth corner hole of the first plate are arranged to correspond to the first corner hole, the second corner hole, the third corner hole and the fourth corner hole of the second plate, respectively; and wherein the heat exchange core comprises a length side and a short side, the first corner hole and the second corner hole of the second plate are in communication with each other, and the first corner hole and the second corner hole of the second plate are located at two ends of the length side of the heat exchange core respectively; a blocking member is arranged between the front surface of the second plate and the back surface of the first plate, the blocking member is located between the first corner hole and the second corner hole of the second plate, one end of the blocking member is located at the length side of the heat exchange core, and the first corner hole of the second plate is in communication with the second corner hole of the second plate by rounding another end of the blocking member; and the heat exchange core further comprises fins, each of the fins is arranged between the front surface of the second plate and the back surface of the corresponding first plate; characterised in that there is no blocking member provided between the front surface of the first plate and the back surface of the second plate; wherein the fin is further provided with a notch, the blocking member is arranged at the notch, and the notch is in a clearance fit with the blocking member; and the blocking member and the second plate are of an integral structure, and the blocking member protrudes from the front surface of the second plate by a height equal to a height of the fin. the heat exchange core comprises first plates and second plates, each of the first plates comprises a front surface and a back surface at an opposite side of the front surface, and each of the second plates comprises a front surface and a back surface at an opposite side of the front surface; portions of the second flow passage are formed between the front surfaces of the first plates and the back surfaces of the adjacent second plates, and portions of the first flow passage are formed between the front surfaces of the second plates and the back surfaces of the adjacent first plates; the first plate comprises a first corner hole, a second corner hole, a third corner hole and a fourth corner hole, and the second plate also comprises a first corner hole, a second corner hole, a third corner hole and a fourth corner hole; the first corner hole, the second corner hole, the third corner hole and the fourth corner hole of the first plate are arranged to correspond to the first corner hole, the second corner hole, the third corner hole and the fourth corner hole of the second plate, respectively; and wherein the heat exchange core comprises a length side and a short side, the first corner hole and the second corner hole of the second plate are in communication with each other, and the first corner hole and the second corner hole of the second plate are located at two ends of the length side of the heat exchange core respectively; a blocking member is arranged between the front surface of the second plate and the back surface of the first plate, the blocking member is located between the first corner hole and the second corner hole of the second plate, one end of the blocking member is located at the length side of the heat exchange core, and the first corner hole of the second plate is in communication with the second corner hole of the second plate by rounding another end of the blocking member; and the heat exchange core further comprises fins, each of the fins is arranged between the front surface of the second plate and the back surface of the corresponding first plate; characterised in that there is no blocking member provided between the front surface of the first plate and the back surface of the second plate; wherein the fin is further provided with a notch, the blocking member is arranged at the notch, and the notch is in a clearance fit with the blocking member; and the blocking member and the second plate are of an integral structure, and the blocking member protrudes from the front surface of the second plate by a height equal to a height of the fin.