Abstract: Annular flow is a typical gas-liquid two-phase flow pattern, where strong fluctuations and shear effects between the gas-liquid phases increase the complexity of flow characteristics. To explore the details of annular flow and accurately to predict the annular flow field, the present work proposes a new numerical prediction method – thin liquid film method (TLFM), which uses Euler-Lagrange method and Euler Wall Film model (EWF) to study the gas phase, droplet and liquid film in the flow field, and the interaction among them. The TLFM analyzes the droplet entrainment and deposition processes, derives the expression of the droplet entrainment from the microscopic level, and provides the calculation formula for entrainment fraction. The TLFM is used to numerically simulate classic annular flow experiments in public literature. Analyzed are the liquid film thickness, entrainment fraction, entrainment rate, Sauter average diameter, pressure gradient, and wall shear stress. The mean absolute percentage error (MAPE) of each parameter predicted by the TLFM is within 25%.