Abstract: This paper discusses the problems existed in active-fault exploration, in the area of breakpoint based on ground reflection seismic exploration, making use of Cross-well Seismic Tomography to detect active-fault and determine the depth of Up-breakpoint and deduced its activity era. It describes the application status of the Cross-well Seismic Technology and introduces some algorithm of Cross-well Seismic Tomography, also in actual test; discussed the data acquisition and data processing methods for Cross-well travel time tomography. Using Curved-Ray tracing algorithm obtained the P-wave velocity structure image across the Luhuatai buried fault. This study shows that the result is highly similar to drilling profile.