The geological structure of Dongpu Depression is complex, with multiple faults, deep burial, thin sand bodies, and unstable sandstone mudstone interbedded sections, which poses great challenges to the exploration and development of long horizontal sections. A biomass based drilling fluid system adapted to Dongpu has been developed with modified vegetable oil as the core. The performance evaluation results show that the system has a temperature resistance of 180 ℃, HTHP ≤ 5mL, ES ≥ 700v, a rolling recovery rate of 98.32% after 16 hours, and a linear expansion rate of 0.817% after 72 hours. It has been successfully applied in 9 wells on site, demonstrating strong long-term stability against high temperatures, a flow pattern of "low viscosity and high shear", and good rock carrying and sand carrying capacity. The rock carrying index is greater than 1.5, and the highest application temperature is 156 ℃. It effectively solves the problems of instability of the Shahejie Formation wellbore, difficulty in carrying rock and sand in long horizontal sections, and directional pressure of thin layers. It has good prospects for application and promotion.