Abstract: High strength steel has been gradually applied in construction industry.As the strength of steel increases,the property of toughness degrades to some extent,particularly in the case of application at low temperature.Therefore,it is necessary to study the impact toughness of high strength steel.Impact toughness tests of 14 mm thick Q460-C steel at low temperature were performed,Charpy impact power level was compared with that of 60,90,120,and 150 mm thick Q345 steel at the same temperature respectively,besides the scanning electronic microscope of the Charpy-type specimen fracture surfaces with different temperature points were analyzed.And the results showed that:1)The impact toughness of Q460-C steel decrease with the descending temperature;2)Between 20 ℃ and-20 ℃,the low temperature impact power level of 14 mm thick Q460-C was lower than that of 150,120,90 mm and 60 mm thick Q345 at the same temperature;3)The influence of steel strength on low temperature brittleness of Q460-C was less obvious than that of steel depth on that of Q345;4)The fracture appearances of Charpy-type specimens of Q460-C,which break at-20 ℃ had finished the transition form ductile to brittle on the whole,with a large of significant brittle characteristics.Meanwhile,a Boltzmann function fit analysis was made on Charpy impact test results of Q460-C,obtaining-11.1 ℃ as the brittle ductile transition temperature.Test results showed that the low temperature brittleness of Q460-C and its welding seam were apparent,to which much attention should be paid.