The semi welded plate heat exchanger is composed of a pair of plates, and each of the two plates is laser welded to form a pair of plates. It is sandwiched between the fixed pressing plate and the movable pressing plate in a superimposed manner. The mesh contacts are formed between adjacent plates and supported by each other, and the rigidity of the plates is remarkably enhanced. Our semi welded plate heat exchanger adopts advanced laser welding technology, which has the advantages of small welding deformation, small residual stress and high quality.