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.