Abstract: Aiming at the problem that the measurement accuracy and stability of the electromagnetic flowmeter are easily affected by the flow pattern when measuring the gas-liquid two-phase flow, this paper proposes a gas-liquid two-phase flow measurement method using the electromagnetic flowmeter under phase-isolation state. A cyclone was used to shape the irregular two-phase flow inlet flow pattern into a gas core-water ring flow, ensuring the orderly distribution of the weight function. Void fraction was introduced to modify the electromagnetic flowmeter measurement model to improve the measurement accuracy. Using air-water two-phase flow as the medium, the measurement method was verified through laboratory experiments. The results show that the liquid phase measurement error of the electromagnetic flowmeter is within ±5% under phase-isolation state. The research conclusions of this paper provide a good idea and method for gas-liquid two-phase measurement in industrial production, and have good application value.