The mechanism and the design parameters for blast with air-decking is studied. The theory of detonation waves is adopted to investigate the processes of the one dimension expanding of the detonation products and motions of plane detonation waves within borehole. Interactions of a rarefaction wave with a interface and reflection on a rigid wall are also analyzed. The same courses of a shock are investigated. It decides the distribution of the pressure of explosion products changing with time along blast hole. Based on the up theory analysis

two conditions should be meeting for a reasonable range of the value of the air-decking ration in blasting rock. First

the ratio adopted should assure that the rarefaction wave from the contact interface between detonation product and air should reach to the bottom earlier than that of the reflected shock wave from the end of the stemming. Second

it also should assure that the reflected shock wave should be reach to the contact interface between detonation products and the air earlier than that of the reflected rarefaction wave from the bottom of the blast hole. Finally

a reasonable value for the air-decking ratio is decided theoretically in air-decking blasting. For different explosives

the reasonable range for air-decking ratio varies from 0.15-0.4. This result is well consistent with the values obtained from site carried out by previous researchers.