Many deep buried super long tunnels are designed for the SichuanTibet Railway line, and most of them are located in high altitude, high steep slope and no man mountain zones above the snow line, where the terrain is steep and undulating, and the traffic conditions are poor. Horizontal directional drilling along the tunnel axis provides an effective method for tunnel investigation. In view of the engineering and geological characteristics, this paper provides a 3000m capacity horizontal directional drilling plan for super long tunnel investigation in terms of equipment and technology. The hole profile is specified in the plan together with full face drilling and coring drilling technology, drilling fluid measures and some measures for complex situations. With less amount of drill work, the plan provides more detailed physical geological data for tunnel investigation, hence the true characterization of the geological conditions in the tunnel.