Abstract: Experimental studies on single-phase real time flow resistance characteristics under unsteady flow condition were carried out. The experimental phenomena show fluctuation changes friction pressure drop characteristics. The friction pressure drop fluctuates with fluctuation flow and there is phase difference between two fluctuation signals. Based on analysis, such conclusions can be achieved that the acceleration may strongly influenced friction pressure drop, and with the same flow rate, the friction pressure drop is different with different directions of acceleration. When the direction of acceleration is same as that of flow rate, the friction pressure drop is large, when the acceleration is opposite with flow rate, the friction pressure drop is small. Based on theoretical analysis, an empirical correlation was obtained to calculate real time friction pressure drop of fluctuation conditions and calculated results fit well with experimental data.