A flow meter comprising a tubular main-body and a cover plate formed by printed circuit board which carries two pressure sensing devices tightly packed by soft rubber material for sensing the pressure head of and the pressure difference between the inlet and outlet of the flow meter. Since the cover plate is mounted on, and fastened to the main-body by fastening screw, but not by adhesive to form a complete unit, the cover plate can therefore bear high fluid pressure without crack or damage, i.e., shall increase the capacity of bearing pressure, the service life and accuracy, and decrease the occurrence of malfunction to the flow meter.