Abstract: The dynamic tension and fracture toughness tests on structural steels(16Mn and Q235B steel)were carried out at room temperature,the results show that:for 16Mn and Q235B steel,both the yield strength and tensile strength increase and the plastic properties of the two kinds of material decrease a little under dynamic loading.The toughness of the base metal and welded joints of 16Mn steel under dynamic loading is higher than under static loading at room temperature.The fracture toughness of welded joints for Q235B steel is poor under static loading at room temperature.Dynamic loading has great effect on the fracture toughness of base metal.The fracture toughness of base metal of Q235B under dynamic loading decreases to one fourth the toughness under static loa-ding.All of the results show that the resistance to dynamic load such as earthquake of Q235B steel is rather poor.From the research in this paper,we can conclude that for material of low level toughness,the tensile pro-perty of material should be considered when studying the fracture behavior under dynamic loading.