In order to cooperate with the further study on stability against sliding in dam foundation of Wudu reservoir, and ascertain the characteristics of the weak structural plane such as fault fracture zone, inter-laminar dislocation band and low-angle fracture, diamond drilling technology was adopted by fitting with SDB double stage and single action diamond drilling tool with two-halves barrel. Coring recovery rate was 100%, the undisturbed rock samples provided reliable basis to the study on stability against sliding.