Abstract: Using the dynamic caustic-test system, the PMMA model transmission-type experiment of dynamic caustics was carried out to simulate the blasting process of rock with joints. Varieties of dynamic intensity factors in the crack-tip field, extensions of cracks going through the joint planes for different distances between hole and joint were analyzed especially under the condition that the initial cracks and joint planes had different separation angles. Experimental results show that the dynamic intensity factor of the crack-tip and the extension speed decrease dramatically while the cracks go through joint planes but afterwards the intensity factor increases, that when the crack goes through the joint plane, it can deviate a short distance along the joint, and then continues to develop in its initial direction with respect to the appropriate distance between hole and joint.