When shale gas reservoir is developed by horizontal wells，due to casing eccentricity and irregular diameter，the displacement efficiency of oil-based drilling fluid is usually low. Some oil-based drilling fluid is mixed into cement slurry，which affects the performance of cement slurry. In order to improve the anti-pollution ability of shale gas cementing cement slurry，the surfactant （AFSG-1） was prepared by mixing non-ionic surfactant and anionic surfactant in the laboratory. The research on improving the anti-pollution performance of shale gas well cementing cement slurry by AFSG-1 was carried out with the field oil-based drilling fluid and cementing cement slurry as the research object. The results showed that the addition of oil-based drilling fluid in the field would seriously affect the fluidity，thickening time and mud-mixed water and debris properties of cement slurry. The greater the proportion of oil-based drilling fluid，the more serious the pollution was. With the increasing amount of AFSG-1 in cement slurry，the anti-pollution ability of cement slurry was gradually enhanced. When the mass fraction of AFSG-1 in cement slurry was 2%，and then 20% oil-based drilling fluid was added，the fluidity，thickening time and cement stone properties of the slurry were significantly improved compared with those without surfactant. In addition， the anti-pollution performance improvement effect of AFSG-1 on oil-based drilling fluid of cement slurry was significantly better than that of other commonly used surfactants. AFSG-1 could effectively improve the ability of shale gas cement slurry to resist the pollution of oil-based drilling fluid， improve the cementing quality and ensure the cementing safety.