Low-carbon high-strength steel and preparation method thereof

The invention relates to low-carbon high-strength steel and a preparation method thereof. The low-carbon high-strength steel comprises the following chemical components in percentage by weight: 0.06%-0.09% of C, 0-0.15% of Si, 1.70%-1.90% of Mn, 0-0.012% of P, 0-0.002% of S, 0.055%-0.080% of Nb, 0.01%-0.03% of V, 0.10%-0.14% of Ti, 0.10%-0.15% of Mo, 0-0.004% of N, 0.01%-0.06% of Als and the balance of Fe and inevitable impurities. The preparation method comprises the steps of smelting; performing refining; continuous casting; heating is performed; rough rolling; finish rolling; carrying out laminar cooling; performing coiling; flattening is conducted; and tempering. The metallographic structure of the low-carbon high-strength steel provided by the invention is bainite and ferrite, wherein second-phase precipitated particles with the particle size being smaller than or equal to 10 nm account for 15-20%; the yield strength ReL of the steel is larger than or equal to 750 MPa, the tensile strength Rm is larger t