Abstract: As compared withpolymers, surfactant is at present the most promisingdrag-reducing additive because of its long service life and theadvantage of freeing of mechanical and heat degradation. Althougha large amount of experimental studies, theoretical analyses andnumerical simulations were performed on surfactants turbulentdrag-reduction, no convincing conclusion has been drawn yet. Thispaper summarizes major characteristics of turbulent flows such asthe mean velocity profile, velocity fluctuation intensity profile,correlation coefficient and turbulent stress profile. It isgenerally believed that the inhibition of wall-normal turbulenceintensity and the decrease of Reynolds stress due to thede-correlation between the two fluctuation velocity componentslead to the drag reduction in surfactant drag-reducing flows. Theproblems existing in the current researches are analyzed, and somesuggestions are put forward for further studies.