Abstract: Surface tension of polyether surfactant (PEO-PPO) with various chain structures was measured by surface tension measurement,and the local structure at the air/solution interface was investigated by the Sum Frequency Generation vibrational spectroscopy(SFG).The relationships between the locally interfacial structure and the surface activity of PEO-PPO surfactant were elucidated.The closely packing of PPO segments and well-ordered orientation of methyl group at the air/solution interface are responsible for the surface tension reduction of polymer solution.With the increasing of solution concentration and the molar ratio of PPO and PEO blocks(n_PPO/n_PEO),more PPO segments were segregated onto the surface and closely packed,and the methyl groups in PPO units orientated more orderly.Meanwhile,the copolymer with PPO block at the chain ends is easier to enrich to the surface,and thus is more efficient to reduce the surface tension.