This paper introduces drilling operation of and some key technologies used in the borehole WFSD-4 of Wenchuan Earthquake Fault Scientific Drilling Project. The main drilling technologies used in the drilling operation of WFSD-4 are positive displacement motor-hydraulic hammer-long split core barrel coring technology, eccentric reaming coring technology, anti-erosion core bit technology, high angle directional drilling technology, retrievable casing technology, the new type of drilling fluid system and new type of drill rig for deep hole coring.