The measurement of the flow rate of various liquids and gases is critical in industrial automation. Positive displacement flowmeters (PDFs) are highly accurate flowmeters that are relatively insensitive to the upstream velocity distribution and fluid viscosity. This paper presents a high-pressure PDF containing a pair of internal cycloid rotors, with the advantages of large displacement, compact structure, high accuracy and small pressure loss. Flow coefficient curve of the prototype fabricated as the part of this research is given, and the reasons influencing the accuracy of the PDF are analysed deeply. In order to further improve the accuracy, the flow coefficient is corrected by linear function. Several experiments were performed to confirm the measurements over a flow range of 1~100L/min with relative errors of less than 0.3%.