Large holespacing and small burden blast can enlarge the angle of crater,produce an arc free face beneficial to the intensification of reflecting tensile stress and the distribution of volocity field,anhance the utilization of blasting energy and improve blast efficiency,the parameters of hole patterm are better to be defermined by the test of double hole explosion crater and in light of the principle of free face with equal resistance.The holes are full changed and laid out in triangle,and the time of millsecond delay priming between rows can be estimated with semi expiric formula.