Oil-water two-phase flow is the main fluid form in petroleum industry. Since it is associated with safety operation and economic benefit, the flow velocity needs to be measured accurately. A method based on continuous-wave ultrasonic Doppler and drift-flux model is presented to estimate the overall superficial flow velocity of oil-water two-phase flow. A theoretical correlation combining velocity profile and drift-flux model was proposed to relate the measured velocity in the sensing volume of the ultrasonic Doppler sensor with the overall superficial velocity of two-phase flow. The measuring system consists of two piezoceramics ultrasonic transducers with a center frequency of 1 MHz and a PXI-based data acquisition system. Dynamic experiments involving five typical flow patterns were performed in a horizontal Plexiglas pipe with an inner diameter of 50 mm. The results show that the measuring system and the proposed method estimate the overall superficial flow velocity with an average error of 2.27%.