The invention discloses an online measurement and calibration device for oil-gas-water multiphase flow, which comprises a single-phase oil calibration system, a single-phase water flow calibration system, a single-phase gas flow calibration system, a heating buffer tank, a screw pump, a static mixing device, standard meter, meter to be tested, pressure sensor, first temperature sensor, first regulating valve, first ball valve, separator, first quantitative plunger pump, second quantitative plunger pump, the device realizes modularization Management, fully automated operation, used to simulate the flow pattern, flow rate and ratio of the three-phase flow of oil, gas and water at the oil and gas wellhead; it can realize single-phase oil flow, single-phase water flow, single-phase gas flow, gas-liquid Two-phase flow rate, oil-water two-phase flow rate, oil-gas-water three-phase flow rate, oil-water two-phase flow separation phase holdup, oil-gas-water three-phase flow separation phase holdup calibration, calibration and other functions to simulate the working conditions of real oil wells , to provide experimental support for the development of multiphase flow metering instruments.