Abstract: By using dynamic photoelatic method, the dynamic stress field in semi-infinite elastic medium due to contact explosive loading was studied. More emphasis was placed upon the comparison of the transient stress distributions in a finite plate under two kinds of loading conditions: charges concentra ted on one side of the plate and charges symmetrically placed on two opposite sides of the plate. The test results indicated that when using same amount of charges, symmetrically placed charges could stimulate stress concentrations in certain parts of the plate and therefore cause the plate to fracture.