We have investigated the magnetic flux motion in a high quality YBCO disc induced by a pulsed magnetic field in the presence of a static bias field at 77 K. The flow rate R_f was obtained as a function of static bias field. The flux tends to move more easily as the magnetic field is increased, presumably due to the fact that the pinning force is depressed. The flow resistivity ρ_f and the viscosity coefficient η were also estimated as a function of magnetic field.