Based on the electromagnetic wave propagation theory, this article designs a phase sensor to measure void fraction. By adding a phase mixer to the front of the sensor to convert it into homogeneous flow, the measurement of the void fraction of the slug flow is achieved, and the mixing dielectric constant under different flow conditions is analyzed. The hybrid dielectric constant prediction models, logarithmic, Rayleigh, series-parallel connection, H-B and Bruggenman, are evaluated comparatively with mean absolute percentage error of 41. 51% , 6. 07% , 80. 45% , 62. 51% , and 56. 7% , respectively. A new weighted mixed dielectric constant prediction model is proposed for the slug flow, and the mean absolute percentage error is 4. 37% , with 71. 43% of the data within 5% of the mean relative error. Based on the experimental model of void fraction based on homogeneous flow under the same flow conditions as the reference true value in the experiments of the slug flow model, the results of the void fraction solved by the hybrid dielectric constant prediction model proposed in this article are verified and evaluated. Results show that the mean absolute percentage error of the void fraction prediction model is 0. 34% .