Abstract: Based on the data of two-phase flow in narrow rectangular channel, the influence of the two-phase flow friction characteristic under the different fluctuant states was analyzed. Through analyzing the experimental data, it is shown that the fluctuant amplitude of the friction pressure drop is affected slightly by the fluctuant period in narrow rectangular channel, but the frequency of the friction pressure drop fluctuation is changed. However, the change of fluctuant period is of little effect on the average frictional pressure drop. Comparing the φ²_l(φ²_g) -X variation curves at static condition with the ones at fluctuant condition, using the L-M method, it’s found that the two-phase frictional pressure drop in the narrow rectangular channel under the fluctuant state can be calculated by the φ²_l(φ²_g) -X variation curve at static condition.