Abstract: The tensile properties, microstructure and fracture morphology of high strength low alloy steel plate HC340LA were studied at four strain rates (10-3, 5, 50, 200 s-1). The results show that the test steel had better plasticity, higher tensile strength and yield ratio when tensiled at high strain rates (5, 50, 200 s-1) than in quasi-static tension (10-3 s-1). The plasticity and tensile strength decreased during high speed tension with the increase of strain rate, because the ferrite decreased in grain size, distributed unevenly and the grain boundaries increased. The rupture of HC340LA steel plates followed ductile fracture mechanism. The fracture with the strain rate of 50 s-1 displayed uniform dimples which was bigger and deeper, compared with the strain rate of 200 s-1.