Niutoushan deep drilling CUSD3 belongs to the longcan engineering of china national nuclear corporation, which is second deep drilling of xiangshan fundamental geological research project. Drilling strata includes porphyroclastic lava, rhyolitic dacite, schist, slate and phyllite. The Strata is broken, fracture developed, and severe sloughing, resulting in poor stability of hole wall. According to the problems in drilling construction, select the Polymeric solid free drilling fluid, which has the characteristics of good wall protection, good fluidity, and high efficiency of reducing obstacle. The application in Niutoushan deep drilling CUSD3 achieved good effect, and effectively ensure the scientific drilling successfully completed.