The gasketed plate heat exchanger is formed by a plurality of stamped corrugated metal sheets at regular intervals, which is surrounded by gaskets, and pressed by a frame and a compression screw. The four corner holes of the plate and the gasket form a fluid . The piping and the collecting tube are simultaneously separated from each other reasonably, so that they flow in the flow paths on both sides of each phe plates, and heat exchange is performed through the heat exchanger plates. The optimal design calculation of the plate heat exchanger is to determine the model, flow and heat transfer area reasonably under the condition of known temperature difference ratio NTUE. so that NTUp is equal to NTUE.