SY-1 geo-thermal mineral water well in Yingshan， Sichuan Province is a key exploration well for geothermal resources with actual drilling depth of 2758m. It was found that the lithology of the thermal reservoir of Xujiahe Formation in Upper Triassic is mainly feldspar sandstone and siltstone， with buried depth of 2220 to 2758m and thickness of 538m. The Xiashaximiao formation consists of gray-green shale and dark purplish red silty mudstone mixed with yellowish brown medium-thick layered siltstone and massive fine-grained feldspar sandstone， which contains a mixture of high-pressure gas and brine， where complex drilling problems such as well collapse， well kick， overflow， lost circulation and wellbore contraction were encountered. Lab research was carried out on control of rheology， anti-sloughing and stability of high-density anti-sloughing drilling fluids， and with premium sodium bentonite as drilling fluid base， the coating agent， the fluid loss reducer （salt-resistant）， the anti-sloughing agent， and other materials were selected to obtain the final formula of high-density anti-sloughing drilling fluid： water+4% bentonite+0.1% soda+0.1% sodium hydroxide+1% to 2% tackifier HN-1+0.2% to 0.5% environment-friendly macromolecular coating agent+1% to 3% environment-friendly filtrate reducer HJ-1+1%~3% salt-resistant filtrate reducer HLY+1% to 2% environment-friendly anti-collapse agent HFJ+barite. The formula has adjustable density of 1.50 to 1.80g/cm³， infiltration loss of 4.0ml， good rheological property， and remarkable anti-collapse effect； and has been successfully applied in the field and ensured the smooth implementation of the project.