The overpressure of shock wave in a certain distance for the blast-resistant experiment of steel box girder scale model was measured.The TNT equivalent of the homemade composite explosive(TNT/RDX=40/60)and the overpressure values of corresponding location was analyzed and calculated(1,2).The reasonable formulae of the calculation of shock wave overpressure for the experiment was found(3); the overpressure of shock wave of corresponding location is simulated by the finite element software AUTODYN,the measured values were compared with the theoretical calculation values and simulation values.Thus verified throung the rationality of the theoretical formula and the simulation parameters selection.Further,the condition 1 of the explosion test for steel box girder scale model was simulated,and a basis for the numerical simulation was provided for the next step to carry out the Steel box girder of blast-resistant performance.