Long distance horizontal directional drilling technology is applied to geotechnical engineering investigation. By using its advantages of traversing construction and trenchless， it can effectively make up for the shortcomings of vertical drilling method， and because of its good guiding performance， the investigation accuracy is high. Combined with the geotechnical exploration project of the water delivery tunnel of Yangtze-replenish-Han Project， this paper sorted out the use of drilling rig， measurement equipment while drilling， drilling tools， etc.， and proposed the construction technology method of “core drilling+directional drilling” alternating in the drilling implementation process， and finally introduced the construction difficulties and countermeasures in the actual construction process.