Abstract: To predict the critical heat flux (CHF) of low pressure and low flow rate annular flow, a film dryout model considering the evaporation of liquid film and the deposition and entrainment of droplets was established. And the film dryout model was checked by the existing experiment data. The results show that the CHF calculated results are well accord with the experiment data in range of experiment parameters, and the relative deviation is less than 25%. Based on the annular flow CHF model, the impact of the inlet enthalpy difference, mass flow velocity, annular flow diameter and heated length on the CHF was researched. The model could be used to calculate CHF of low pressure and low flow rate annular flow effectively, and could be used to analyze the trend of CHF variation with different parameters.