By numerical simulation, the researches of effecting initial crack forming with slotted charge blasting are performed. The effecting factories conclude radial uncoupled parameter α and seam width W. Herein α adopts 1.43, 1.67 and 2, and 4, 6, 8 and 10 are adopted by W separately. The pressure peak is 15.5 GPa under α=1.67, and formed long cracks. With 6 and 8 mm seam widths, energy focus phenomenon is remarkable. The results show that initial damage of rock are decided by peak pressure of gas and function time. The seam width has significant effect to initial damage. With W adopting 6 and 8 mm, effective energy propagation is ensured and excessive damage area is avoided. The experiments validate the simulation results.