The Shiqianfeng， Shihezi and Shanxi formations in the Yan’an eastern gas field are hard and brittle， with well-developed fractures and high mudstone content. Well collapse and lost circulation often occur during drilling， which greatly increases drilling costs. By analyzing the characteristics of the Upper Paleozoic strata in this area， the mechanism of borehole failure， and the characteristics of the reservoir， a research on a film-forming drilling fluid system with strong inhibition and strong sealing was carried out. With the selection of fluid reducer RHPT-1 and film-forming agent CMJ-2， the formula of film-forming drilling fluid was determined and the system performance evaluation was completed. The results showed that the extreme pressure lubrication coefficient of the system was 0.0659， the cuttings rolling recovery rate was 95.94%， and the 16h linear expansion rate was 8.18%， showing good lubricity and inhibition. It can provide 3% resistance to clay pollution，7% salt resistance， and calcium resistance 2% with stable performance in 100℃ hot rolling drilling fluid， indicating good anti-pollution and thermal stability. It was successfully applied in three horizontal wells， effectively solving well failure in the upper Paleozoic strata in the Yan’an eastern gas field.