The formation in the Xiangyangping area of Guangxi is complex. There are large sections of water-sensitive altered formation and broken formation. Kaolinite and chlorite altered formation is prone to expand and shrink or break off after water absorption, leading to frequent downhole incidents, such as rock falling, borehole collapsing, drilling string sticking or burial. Through the lithological analysis of the core samples from the formation, the film-forming anti-collapsing solid-free drilling fluid system was adopted, which effectively solved the expanding and shrinking problems of water-sensitive altered formation with remarkable enhancement of borehole wall stability and significant improvement of borehole wall protection. As a result, the cores taken out were intact with high core recovery; down-hole incidents were avoided; and drilling efficiency was greatly improved with shorter construction time and less construction cost.