The boiling heat transfer experiments have been carried out in vertical narrow- annularchannels with pure water. A two-dimensional homogeneous turbulence model of boiling flow- hasbeen developed and solved numerically to yield pressure gradient, and velocity, thermal andturbulence fields, together with local heat transfer coefficient along the length of the tube.Predictions are compared with the data of experiments and agreed well with it. The model resultsshow- that the heat transfer coefficient increases as the gap size decreases in annular channels. Thismodel can be used to predict heat transfer of boiling flow- in narrow- channels.