Compared with traditional vertical drilling， horizontal directional wire-line core drilling has higher investigation efficiency due to its technological characteristics in the investigation of tunnels and underground engineering in the difficult mountainous areas in western China. However， due to the complex geological conditions and fragile ecological environment in this area， hole collapse， leakage and other accidents are easy to occur in the drilling process， which requires that the flushing fluid used should have strong inhibition， non-toxic and harmless characteristics while ensuring rheological properties. In view of the performance problems of horizontal directional drilling fluid in wire-line coring， polymer polyols， which are environmentally friendly and easy to degrade and have strong inhibition， are selected as the main research object， and environmentally friendly cellulose and nano-SiO₂ are selected to improve their rheological properties. The developed polyalcohol anti-collapsing flushing fluid system： 2% PVA+0.5‰ MC-9+0.5‰ LE-5+0.1% SiO₂+0.3‰ DD-1+0.2% DS-957+0.8% KCl， composed of environmentally friendly materials， has good rheological property， anti-collapse inhibition ability can also meet the requirements of directional core drilling engineering. It provides a new idea to solve the technical problem of flushing fluid in horizontal wire-line coring directional drilling and has reference significance and value for similar projects.