Pre-geological prediction(PGP)is defined as the prediction of engineering geologic condition and hydrogeological condition certain distance ahead of the working face. The purpose of this paper is to introduce mainly geologic survey before and in excavation, to clarify their emphasis on PGP. At the same time, the technique is applied to an engineering case, the longest highway tunnel in Gansu province. Data of geological survey of outside tunnels, sound wave detection, and geologic sketch for both tunnel face and sidewalls within the tunnel are analyzed. After analyzing these data, long-term pre-geological prediction forecasting basic geological conditions of fault 4 such as lithology, scope, location, etc., and short-term and more accurate pre-geological prediction are reported.