Abstract: The relationship between void fraction models and mass flux, pressure and mass quality was analyzed, and the applicability of these void fraction models in boiling pressure drop calculation of rectangular channel was evaluated. The results show that different void fraction models lead to the large discrepancy of gravitation pressure drop and acceleration pressure, however, the proportions of gravitation pressure drop and acceleration pressure in the total pressure drop are very small because the predominant two-phase flow pattern in narrow rectangular channel is annular flow, thus the effect of void fraction model on frictional pressure drop can be neglected. The results also indicate that the relative deviation of frictional pressure drops calculated by Zivi model and other void fraction models is within ±5% and Zivi model is proposed to calculate the void fraction in narrow rectangular channel.