In order to meet the needs of China-made gigantic bridges with long spans, 14MnNbq steel was developed . It is a new type of microalloyed steel. In this paper, simulated controlled rolling and cooling is taken. The role of microalloyed element Nb and Nb(CN) in the process of deformation and their effects on microstructures and mechanical properties of 14MnNbq steel are analysed by means of optical microscope, TEM, electrical chemical phase extraction analysis and micrography analysis.It is pointed out that in period of non-recrystallization of finish rolling should increase the deformation increment as great as possible to give full play to Nb, The cooling speed after rolling and the temperature of finish cooling should be controlled properly according to working condition to ensure Nb(CN) to separate out adequately. It is proved that Nb possesses good fine-grain strenghening and medium precipitate-hardening effects.