To investigate the turbulent drag-reducing mechanism of drag-reducing aqueous solution, turbulent drag reduction of 30×10-6 cetyltrimethyl ammonium chloride (CTAC) aqueous solution in a channel flow was investigated experimentally and the influence of the drag-reducing additives on the flow structures was studied based on proper orthogonal decomposition, and POD was used to analyze turbulent fluctuating velocity based on PIV. The experimental results showed that at different Reynolds numbers, such as, 15×10⁴, 25×10⁴ and 35×10⁴, drag reduction (DR) rate of CTAC aqueous solution can reach up to 651％, 700％ and 330％ respectively, and the CTAC additives can inhibit the ejection motion of low-speed fluid from the wall and sweep motion of high-speed fluid towards the wall associating with turbulent bursting events, that is to say, the CTAC additives can inhibit the formation and development of turbulent coherent structures, resulting in a great decrease of turbulent contribution to frictional drag and DR.