Thermal simulation test, TEM(Transmission Electron Microscope) and nanobeam EDS techniques were used to investigate the dissolving and precipitation behavior in Nb-bearing mciroalloyed steel. The experimental results indicate that: there are two families of precipitates in the as forged samples. The larger precipitates of Nb(C,N) disappear after being held for 2h at 1300°C,while the inclusions of MnS formed from the solidification even remain for 48h held at that temperature. After 30% of predeformtion at 850°C and 900°C, the strain-induced precipitation occurs, that is, the other tiny precipitates. Compared with the samples relaxed at 850°C, the ones that are held at 900°C show larger particles by same holding time but demonstrate the same size when the relaxation time reaches 1000s.