The materials response of a laser beam welded joint from hot rolled DP600 steel plate to the dynamic loading has been experimentally studied by instrumented Charpy impact testing. Based on the impact force-displacement curve, Critical Crack Length, i.e. CCL and dynamic crack extension resistance curve, i.e. J-a were determined, describing the welding joint’s crack formation toughness and the dynamic crack behavior. It is shown that the difference of crack initiation and propagation between the HAZ and BM is not significant. In addition, the CCL of Welding Area, i.e. WA is multiple higher than that of HAZ and BM, which is also less dependent of low temperature. Moreover, the J-a curve of WA consists of two segments, the initial sudden ascending with linear feature and the subsequent slow rising. Furthermore, tearing module derived from the slope of J-a curve was discussed, indicating the material microstructure mechanism affected by the thermodynamic process of laser beam welding.