The effect of reduction on the microstructure refinement and mechanical properties of the as-hot rolled dual-phase Nb-bearing steel were studied at laboratory. It is found that the dual-phase steel displays clearly classic dual phase morphology which is ferrite and martensite or bainsite, and the fine island or lath martinsite is dispersed on the matrix of ferrite by the observation of microstructure. The grain can be refined, and the increased precipitated second particles are fined and dispersed with the increasing of reduction. The mechanical properties determination result shows that the mechanical properties have greatly improved by large reduction. The tensile strength obtained in the laboratory is up to 680MPa, the ratio of yield strength and tensile strength is low, and the elongation is better.