Abstract: Roots flowmeter is a kind of PD flowmeter widely used in the metering of crude oil with a high accuracy. The paper introduces the structure, operating principle of this flowmeter and its advantages and shortcomings. The problems existed in the metering and calibration of crude oil transportation for this kind of flowmeter are discussed. Also, the process design, Calibration and installation of the flowmeter, the leakage of cross valve, the influence of variation of viscosity to calibrated results are analyzed, The suggestions to improve the metering accuracy and regular maintenance are put forward.