Abstract: The low-alloy and low cost wear-resistant HSLA NM400 steel plate with high toughness was developed by Ti-Cr-B micro alloying, then direct rolling at austenite recrystallization zone with low-temperature tempering after quenching. Its mechanical properties, microstructure, fracture morphology and precipitates were tested and investigated by means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the microstructure of specimens is mainly composed of the high-density dislocated lath martensites with carbides distributed on them. The tensile strength≥1400 MPa, the surface hardness≥HV450 and impact toughness at -40°C>60 J. With a good hardenability, the steel has a uniform hardness distribution in thickness direction. In addition to the solid solution hardening and grain refinement, a considerable number of the high-density dislocations and Ti(C, N) nano-precipitates play an effective role in hardening. It was found by SEM and EDS that the brittle second-phase particles in fracture dimples are mainly of MnS and Al2O3, whose biggest size is about 2 μm.