It is disclosed for a kind of system and method for drilling rock core, in particular to determines their orientation in subsurface. Core drilling system includes a drill string, it has the drill bit in its end, a core sampling in its end configures mounted inside drill string, including the core sampling configuration for keeping a core barrel (100) for a core sample, core barrel, its have the first end that is located near drill bit with from the remote second end of drill bit, one core catcher (101), its first end for being fixed on core barrel (100), core tube head (102) in second end fixed to core barrel (100), system further comprises that a rotational joint (104) for connection core barrel is led to releasable lock a to latching unit (105) for drill string is suitable for, wherein the rotational joint (104) allows latching unit (105) to rotate independently from core barrel (100). System further includes an orientation unit (103), it is rotatably to be fixed on or be integrated into latching unit (103) between the rotational joint (104) and the second rotational joint being fixed on latching unit not over the core barrel on the opposite for being located at rotational joint (104) relative to core barrel or the part that rotates freely through as a separation is placed.
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