Abstract: The dynamic fracture toughness of a low carbon alloy steel and welded joint was estimated by the Hopkinson Pressure Bar at different temperatures.The experimental temperature function was obtained and the effect of temperature on dynamic fracture toughness was analyzed.The fracture toughness of matrix metal and welding seam decreased under the condition of loading stress wave(≈106 MPa·m1/2/s).The fracture toughness of matrix metal effect of the was higher than that of the sample with welding seam at the same temperature,because the state of structure on the sensitivity of strain rate was different.A dynamic fracture characteristic analysis diagram with loading stress wave was established based on the temperature effect between matrix metal and the sample with welding seam.The relationship of temperature,board thickness and fracture toughness was discussed.