Research on the mechanism by which surfactants change the wettability of rock surfaces has certain theoretical guiding significance for on-site construction in oilfield. The wettability changing mechanism of oil-wet sandstone surface by anionic surfactant sodium lauryl alcohol polyoxyethylene ether sulfate-1（PES）was studied through the determination of infrared spectrum， morphological scanning imaging，Zeta potential，solid surface oscillation frequency and contact angle. The results showed that compared with the infrared spectrum of oil-wet quartz powder，the infrared spectrum of quartz powder treated with PES had stretching vibration peaks of S—O bond，sulfoxide S=O bond and sulfone —SO₂— bond，indicating that“adsorption”was the wettability changing mechanism of oil-wet sandstone surface by PES. Due to the adsorption of PES on the surface of oil-wet quartz wafer，the surface of quartz wafer was relatively flat and the average roughness was greatly reduced. The Zeta potential of untreated oil-wet quartz particles was -4.2 mV. The Zeta potential value of the sample treated with PES decreased with the increase of PES concentration，and finally tended to equilibrium. The electrostatic repulsion force between PES and negatively charged rock surface made PES adsorb on the sandstone surface with weak intermolecular force. As the concentration of PES increased，the resonance frequency decreasing amplitude of quartz crystal surface became larger and larger，that was，the adsorption amount of PES molecules on the rock surface became larger and larger. In addition，the original contact angle of untreated oil-wet quartz wafer was 140° ，while the corresponding contact angle of oil-wet quartz wafer treated with PES was 109° . With the addition of PES，a double-layer adsorption structure formed between the hydrophobic chain of surfactant and the hydrophobic end of crude oil components. At this time，the hydrophilic head group of surfactant exposed outside，making the contact angle gradually decrease， thus changing the wettability of solid surface.