To explore the drag-reducing mechanism of turbulent water flow with surfactant additives, the drag-reducing features of surfactants are intruduced and hypotheses for the drag reduction mechanism are reviewed. It is indicated that based on LDV and PIV, the appropriate entrance length is important for revealing the turbulent structure and hydrodynamic mechanism of surfactant drag-reducing water flow, and exact measurement of forming time and relaxation time of shear-induced state is necessary for determining the entrance length for creating the full-developed turbulent flow.