During the drilling construction of a geothermal well in Beijing， numerous technical challenges were encountered， including severe mud-making in mudstone， deterioration of drilling fluid performance， hole-wall collapse， and frequent occurrences of pipe sticking and burying accidents. Aiming at the above problems， this paper systematically expounds the improvement scheme of the original drilling fluid system and the engineering application of the bi-polymer anti-collapse drilling fluid. Through laboratory experiments， the performance indexes of the original drilling fluid such as rheological properties， filtration loss， and inhibition were optimized and improved， and the bi-polymer anti-collapse drilling fluid system was gradually transformed from the original drilling fluid and applied on field drilling. The practice has proved that the improved drilling fluid has achieved significant improvements in hole protection effect， rheological characteristics， lubrication performance， and drilling efficiency. The study also points out the limitation such as insufficient efficiency of solid control equipment in the current drilling technology and puts forward targeted technical suggestions， providing an important reference for the drilling fluid design and construction of the similar geothermal well projects.