Abstract: In underground mining and tunneling projects, directional fracture-controlled blasting is critical for precise tunnel formation and reducing over- and under-excavation. However, the presence of well-developed joints in rock masses often disrupts the propagation of directional cracks, affecting mining efficiency and surrounding rock stability. This study adopts theoretical analysis and numerical simulation to investigates the effects of the distance between blast holes and joints, joint thickness, the direction of cutting, and the angle between the cutting direction and the joint affect directional cracks. Methods were proposed for optimizing these parameters and were validated through trial tests. Results show that when the distance between blast holes and joints was controlled within the range of 8R to 12R, it ensured effective crack propagation through the joints without significant impact on the surrounding rock. Increasing joint thickness required higher blasting energy. The joints became impenetrable at 2.4R. When the angle between the cutting direction and the joint were controlled between 60° and 75°, it effectively reduced crack offset and maintained the expected design expansion length. This study provides references for the design of cutting seam blasting in underground projects involving jointed rock masses.