Abstract: A new type of high-strength and high-toughness low-alloy Mn steel was designed by multi-element alloying.The static CCT diagram,microstructure,fracture morphology of the steel,as well as the effect of heat treatment on its mechanical properties,were studied.The results show that the stability of under-cooled austenite in the steel is excellent,which makes the steel have high hardenability and tempering stability.After being quenched at 890 to 930℃ and tempered at 200 to 230℃,the steel obtains tempered lath martensite which makes the steel the optimum combination of tensile strength R_m and impact toughness A_kv (R_m ≥ 1 500 MPa,A_kv ≥ 85 J).A good performance-price ratio was determined by properly increasing the content of Mn which is abundant in China.