Abstract：Based on the acquisition data of drilling process monitoring(DPM) system for diamond drilling in different granite grounds，specific energy of drilling and the corresponding variation characteristics with depth have been analyzed. The results show that the specific energy of diamond drilling(SEDD) increases with the decrease of weathered degree of the rock and is markedly divisional. The value of SEDD is nearly equal to that of specific energy of percussive drilling(SEPD) in moderately weathered granite. However，the value of SEDD is far less than that of SEPD in very strongly weathered granite and greater than that in slightly weathered granite. Obviously，it is reasonable to estimate SEDD by SEPD in none but moderate hard granite，which agrees with the practice of rotary drilling adaptable to the rock formation with moderate hardness or soft rocks. Finally，based on divisional property of specific energy curve with depth，combining the corresponding average value and upper threshold value of SEDD，a real-time classification approach for rock formation has been provided.
