With the great water inflow and high pressure of confined water in ZK311 borehole in a phosphate mine in Guizhou, the inner tube for wire-line coring could not be put down. According to the serious block falling, phosphate erosion, uncertain core collecting rate, quick drilling pipe joint wearing and frequent drilling pipe breaking accident, drilling bit was modified and construction technology was innovated with good drilling and geological results. The paper introduced the drilling technology and the construction measures in this project.