The invention discloses Nb-contained high-strength high-tenacity low-density steel for an automobile and a preparation method of the Nb-contained high-strength high-tenacity low-density steel for theautomobile, and relates to the field of metal materials. The Nb-contained high-strength high-tenacity low-density steel for the automobile comprise, by mass percentage, 0.9% to 1.1% of C, 9.4% to 9.7%of Al, 26.9% to 28.1% of Mn, 0.08% to 0.50% of Nb, smaller than 0.5% of Si, smaller than 0.004% of S, smaller than 0.003% of P, and the balance Fe and other inevitable impurity elements. According tothe Nb-contained high-strength high-tenacity low-density steel for the automobile, a finely dispersed NbC phase is precipitated by adding the Nb element to traditional Fe-Mn- Al-C low-density steel,the NbC phase and kappa-carbide jointly generate a precipitation strengthening effect, and then the high-strength high-tenacity low-density steel excellent in corrosion resistance is obtained, whereinaccording to the high-strength high-tenacity low-density steel excellent in corrosion resistance, the density is between 6.4 g/cm<3> - 6.7 g/cm<3>, the tensile strength is between 980 MPa and 1200 MPa, and the elongation percentage after fracture is between 20% and 50%, and the corrosion potential is larger than minus 0.462V. The Nb-contained high-strength high-tenacity low-density steel is suitable for automobile steel demands, can achieve lightweight of the automobile and meets the development concept of energy saving and emission reduction.