Abstract: Natural rock mass usually contains discontinuous medium in geological structural planes such as joints，fissuring，faults etc.The discontinuity of rock mass has both important influences on the spread of stress wave and the formation of pre-cracking during the pre-splitting blasting.In order to investigate the effect of angle of joints strike on the cut-through degree of the pre-crackings，the segmented blasting vibration tests for the pre-crackings generated are made during once pre-splitting blasting.It has been found through the angle of joints strike and the decreasing vibration rate of different sections that the angle of joints strike between blast holes has a significant influence on pre-cracking；the bigger the angle of joints strike in the location of the pre-splitting blasting，the higher the decreasing vibration rate of the generated pre-cracking at that location.The cut through degree is increased as the angle of joints strike increases.Through observing the effect of pre-splitting blasting on site，it is clear that when the angle of strike of joints plan gets close to 90°，the pre-cracking will have a best penetrating and flatness，which is almost consistent with the theoretical analysis.

Key words: Pre-splitting blasting, Pre-cracking, Jointed rock mass, Joint surface angle of strike, Segmented decreasing vibration test