Abstract: Adopting digital laser dynamic caustics experimental system,research two mutually to expand crack dynamic characteristics and interaction relations under explosion loading. The results showed that:process relative to the propa- gation of the crack can be divided into three stages:independent extension,repel each other,attract each other,eventu- ally forming connections to form each other,this feature is not change with the crack initial vertical distance under this experimental condition;Crack propagation speed increase sudden when the crack interact in the process of the exten- sion of crack,and the two horizontal distance of the crack tip decreases with the increase of crack initial vertical dis- tance when the crack propagation speed increase;With the change of the two crack initial vertical distance,the two cracks begin interaction when the crack tip on the between 56-70 mm;The largest vertical migration distance of crack position corresponding to the crack tip horizontal distance of zero moment,resulting from relative movement between two initial crack spacing in the vertical direction of the greater the offset distance,the smaller instead.