During the drilling operation of Wenchuan earthquake fault science drilling project (WFSD), due to stratum breaking, borehole shrinkage and borehole walls' collapse, drilling accidents occurred frequently and core recovery has been low. In the borehole section of WFSD-2, where the core recovery was poor, sidetracking technology was used to get better core recovery and core quality. During the drilling of WFSD-4 hole, pipe stuck accidents occurred within the casing, casing sidetracking technology was used to by pass the obstacle in the hole. This article describes the casing sidetracking technology used in complex formations, referring to the technical measures adopted from preparation to implementation period. The successful application of sidetracking save project implementation time and cost, this will be good guidance and reference for future similar operations.