Abstract: The effect of two-pass defonnation-first pass 60% , 20 s^-1, second pass 20% , 10 s^-1 at 850〜1 050 ℃ and different holding time (10 ~ 50 s) between passes on recrystallization of Nb microalloying low carbon bainitic steel (0. 21C, 1. 50Cr, 0. 20Mo, 0. 047Nb) and the interaction between thermal-deformed austenite recrystallization and strain- induced precipitation of Nb( CN) have been studied by Gleeble-2000 thermal simulation test machine. Results showed that with defonnation of steel at 1 000 ~900  ℃ for 10 s, the strain-induced precipitation of Nb (CN) began to delay austenite recrystallization process； and ≤10 μm austenite grain size could be got by two-pass deformation.