The invention discloses a three-phase metering device and method for high-water-content low-yield oil well output liquid. The device comprises a primary rotational-flow device, a gas nucleus samplingpipe, a secondary rotational-flow device, a steam trap, a rotational-flow type oil-water separator, a water-blocking filter screen type oil remover, a water-filtering pore plate and a separated oil buffer tank which are sequentially connected from bottom to top, wherein a gas-liquid rotational-flow separator is arranged in the gas nucleus sampling pipe. The multiple-stage rotational-flow devices are utilized, a rotational-flow forced flowing means is adopted, the application range of oil well output liquid separation is increased, and the three-phase metering device and method are suitable forstratified flow and wavy stratified flow at low flowing speed and is also suitable for annular flow and slug flow at high flowing speed. The three-phase metering device also comprises temperature andpressure sensors for separated gas and temperature and pressure sensors for main pipeline oil water so as to obtain temperature values and pressure values and verify the density and volume parametersof oil, gas and water three-phase fluids.