The invention relates to an oil-gas-water multiphase flow calibration system and an oil-gas-water multiphase flow calibration method. The oil-gas-water multiphase flow calibration system comprises a metering tank. The measuring tank comprises a tank body and a dome, wherein a connecting pipe for conveying oil-gas-water-containing three-phase fluid into the measuring tank is connected to the side wall of the tank body, and a precise height scale is further arranged on the side wall of the tank body. The dome is provided with a pipeline for gas circulation, and the pipeline is sequentially provided with a filter and a thermal gas mass flow meter for measuring gas flow. The oil-gas-water multiphase flow calibration system and the oil-gas-water multiphase flow calibration method provided by the invention are advantageous in that the problem of oil-gas-water three-phase outlet flow calibration of a multiphase flow simulation system can be solved, and the flow of each phase can be provided accurately in a real-time on-line way, and at the same time, a multiphase flow calibration experiment is more visual and reliable.