Abstract: A mathematical model for predicting the pressure drop characteristic of gas-liquid two-phase annular-mist flow through an annular narrow passage is presented. The flow model takes into account the compressibility of the gas core fluid, the phase slip and droplets entrainment in the gas core flow. The assumed vena contracta effect of the mist core flow through annular narrow passage is considered by applying discharge coefficient for pure air flow. A force balance method is applied to spherical droplets to calculate the phase slip ratio of the mist core flow at the throat cross-section of the annular narrow passage. The effects of two-phase mass flow rate and mass flow quality on pressure drop, cross-section area of the core flow at throat, relative variety of droplet velocity are disscussed in detail. To verify the proposed model the computed two-phase pressure drop is compared with experimental data of air-water mixture for different annular narrow passages and different inlet conditions,and a good agreement between the simulation results and experimental ones is obtained.