The impact toughness and fracture toughness of laser-MIG hybrid welding joints of A7N01S-T5 aluminum alloy for high-speed trains under the temperatures of 20 ℃,0 ℃,-20 ℃,-40 ℃ and -60 ℃ were carried out. The results showed that at the same temperature,the impact toughness and fracture toughness of the heat affected zone（HAZ） was the best,the base metal（BM） was the second,and the weld metal（W） was the worst. With the decrease of temperature,the impact toughness and fracture toughness of the three zones（HAZ,BM and WM） of laser-MIG hybrid welding joints had been improved to a certain extent,but the changes were small.The size of toughness dimples on fracture surface in the heat affected zone and the base metal were larger than that of the weld metal. During the fracture process,large dimples could produce large deformation to resist the crack growth,absorb more energy,and show good fracture toughness.