Abstract: In this paper, the structure and theory about the vibrating-wire viscometer were introduced.The viscosity and density of fluids can be measured simultaneously by this apparatus in wide ranges of temperature and pressure.The reproducibility and accuracy of this instrument were determined using n-pentane as the test fluid.At the same time, the viscosities and desities of cyclohexane (323.15—413.15 K), n-octane(313.15—393.15 K) and benzene (303.15—445.15 K) under normal pressure and 6.10 MPa,respectively,and isooctane (298.15—403.15 K), n-heptane (298.15—403.15 K) under normal pressure and 5.10 MPa,respectively,were measured.The experimental data of viscosity and density were correlated with temperature.