In order to solve the problem that the large-bore and deep-hole blasting in the open air generally has a large block rate, a central air-spaced charge is used instead of the original continuous charge. Based on the Ansys / Ls-dyna finite element software, when the upper and lower charge ratios were respectively 1:4、3:7、2:3and 1:1,the calculation models which air separation ratio is 10%、15%、17.5% and 20% of the length of the blast hole were established for analysis.When the loading ratio is 3:7 and the air separation ratio is 15%, there is no excessive stress concentration in the hole wall pressure,the average pressure is the highest and the high pressure action time is long, which is conducive to the uniform distribution of the fragmentation of the rock. At the same time, the calculation models for the gun bore density coefficients of 1.4、1.6and 1.75 were constructed, and the above conclusions were verified.