A wide range of fracture zones and water-rich areas commonly exist along the axis of the tunnel in the long and deep buried tunnels of water conservancy projects， the management of pre-grouting by more than 1000 meters of ground horizontal directional drilling can achieve a good effect of the surrounding rock reinforcement and gushing water blocking， which has been a successful attempt in the water conservancy industry. This paper introduces the successful experience of drilling ultra-long horizontal directional pre-grouting holes with screw drilling tools in a project. The difficulties and problems are discussed such as cutting removal， coping with the problem of “back pressure”， measurement while drilling system in strong magnetic field， measures of green exploration， as well as the insufficient adaptability of drill， low efficiency of hard-rock drilling， and the influence of grouting on drilling operation， etc.， and the contermeasures are also posed. 4 main holes and 6 branch holes were constructed， along which the longest hole is 1427m， and the drilling workload is 8737.89m. The implementation of the project proves that the current directional drilling technology has the ability to drill accurately over long distances， which can provide a guarantee for the pre-grouting and ahead-treatment in the complex strata of the ultra-long tunnels and the related drilling projects.