Abstract: Dynamic caustic experimental method and numerical simulation method were used to study the crack propagation rules and the tension/compression damage zone at the end of boreholes in the planar model.The results show that the effect of different length-diameter ratios on the crack propagation was significant. As the length-diameter ratio increasing , the crack propagation lengths increased and the expansion angles decreased.When the length-diameter ratio was 5/5 ,the crack propagation angle was about 90°.When the length-diameter ratio increased to be 20(30/1.5) , the crack propagation angles decreased to be 40°.As the length-diameter ratios increased again , the crack propagation angled didn 't change any more.The numerical results are in good agreement with the experimental results , and Numerical simulation shows that small area of compression damage area formed in the area of the column hole , and“X"type tensile damage zone formed at the end of the hole , which lead to the formation of explosive crack easily at the end of the borehole.The radius of the tensile damage zone was approximately 5 times the radius of the compression zone around the borehole.