Abstract: The low temperature impact resistance of microalloyed S355K2 hot-rolled H-beam at-30℃ was studied,and the fracture morphology, inclusions and microstructure of unqualified impact samples were observed and analyzed by scanning electron microscope and optical microscope. The results show that the mixed crystal structure and Ca, Al silicate inclusions in steel is the main reason for the low single value of low temperature impact energy at-30℃ and large overall fluctuation. The number and size of inclusions in steel can be reduced by optimizing smelting and continuous casting process. The controlled rolling process is adopted in the rolling process, and the controlled rolling process combing high temperature recrystallization zone with low temperature non-recrystallization zone can be realized by adding the cooling water strong cooling process between the flange of the pass frame. The low temperature impact stability of S355K2hot-rolled H-beam steel is greatly improved.