Abstract: The experimental investigation of air-water two-phase flow resistance characteristics in a vertical channel with a 3×3 rod bundle was carried out under atmospheric and room temperature conditions. Eight classical correlations for predicting frictional pressure drop of two-phase flow were evaluated against the experimental data. The experimental results show that the homogeneous model can predict the experimental data well at high flow rates, but with relatively large deviations at low flow rates. Both the Friedel model and the Lombodi-Pedrocchi model are not suitable any longer for the present case. The Chisholm C model, the Zhang-Mishima model, the Chisholm B model, the Mishima-Hibiki model and the L. Sun model can well predict the experimental data with mean relative errors in the range of 20%-30%. The C factor in the Chisholm C model was modified for giving a new correlation to predict the frictional pressure drop of two-phase flow through rod bundles, showing a good agreement with the experimental data.