For low alloy high strength steel H300LA, the mechanical properties were tested by hydraulic servo high-speed tensile testing machine at strain rates of 0.001, 0.1,1, 10, 100, 200,500 and 1000 s-1, and the yield strength, tensile strength and elongation under different strain rates were obtained. Then, the fracture absorption energy under different strain rates was calculated by integral mechanical curve, and the influence laws of strain rate on material properties were analyzed. Furthermore, the fracture morphology and change law of the test specimens under different strain rates were analyzed by scanning electron microscopy, and the fracture characteristics of the material were analyzed. The results show that the tensile strength and elongation of low alloy high strength steel H300LA are positively correlated with strain rate, and have obvious strain rate sensitivity. The fracture absorption energy increases with the increasing of strain rate, and the fracture morphology is dimple. As the strain rate increases, the number and the size of dimples increase.