In geothermal well drilling in Lankao where the depth of the second well section is more than 1500m, the common bentonite drilling fluid system can not meet the requirements, and it is easy to cause sticking incidents. In order to solve the drilling problems, a kind of low solid phase, high lubricating and double polymer drilling fluid system was designed for geothermal well drilling. Field application in 4 wells showed that the drilling process was smooth, which effectively solved the problems such as poor sand carrying capacity, unstable well wall in mudstone formation, large water loss in sandstone formation, thick mud cake, etc. None of the 4 wells met any difficult situation and incident. The drilling results indicate that the drilling fluid system has good compatibility with the formation characteristics in the Lankao area and can meet the needs of drilling works, providing good guidance for geothermal well drilling in the Lankao area.