Air-deck ratio plays a decisive role in blasting engineering. Researchers have conducted extensive work to study the optimal air-deck ratio. But consensus has not been achieved. Especially slotted charge blasting, the study on it just starts. For its complicated physical process in blasting, it is difficult to perform theoretical analysis to obtain the law between blasting result and air-deck ratio. The numerical simulation method is adopted to study the effect of different air-deck ratio on stress distribution at first. And then laboratory tests are carried out to validate the simulation results. The conclusion may be drawn that good directional fracture could be obtained with air-deck ratio 33.3% ~ 50%. The achievement could provide reference for blasting engineering.