Abstract: As a new drag reduction technique for turbulent flow, surfactant has good development and applied prospects in trace heatingsystem of oilfield and that of submarine pipeline. Pressure drop laws of cetyltrimethyl ammonium chloride (CTAC) in round tubewith different diameters are measured, influence of diameter size and concentration of surfactant on drag reduction rate is researched and relation curves between drag reduction rate and Reynolds number under different conditions are obtained.