During the drilling process in the covering layer of Zhumadian area in Henan Province， the Quaternary clay layer， sandy mudstone， loose sandstone unevenly interbedded with mudstone were encountered， resluting in difficult wall protection， prone to accidents such as block jamming， hole collapse and burial， and difficult in taking cores. Based on the geological conditions and the drilling construction data within the area， the dual-polymer anti-sloughing flushing fluid was used. In the on-site application， the stability of the hole wall was good during the drilling process of the long open hole well section， without any incidents of falling or collapes. The core recovery rate can meet the geological design requirements， moreover， the casing depth and construction cost were reduced.