TST advance geology prediction technology, which is based on the mixed model of scattering and reflecting, is adopted in the construction of tunnels in karst areas in Guizhou. Main study results are as follows: 1) The geological conditions 150m ahead of the face of the parallel adit of the entrance section of Doumo tunnel and ahead of the face of No. 1 horizontal adit of Dadushan tunnel are obtained. 2) The distribution, scale and development of the karst fissures and karst caves ahead of the tunnel face are predicted. 3) The prediction results, which coincide with the actual geological conditions, provide accurate geological basis to take support measures in advance. 