Abstract: A 1 mm cold rolled plate of nitrogen bearing martensitic stainless steel 420U6 with reduction 66% was simulated-annealed by the Gleeble-3800 thermo-simulation machine, the recrystallization temperature under a constant holding time and the recrystallization time under a constant temperature were determined respectively by hardness method and metallographic examination, the recrystallization activation energy of the test steel was calculated according to Arrhenius equation. Test results showed that the recrystallization temperature in steel was 664. 2 Y when holding time was 60 s ；the recrystallization time in steel was 7. 7 s when annealing temperature was 780 °C ； and the calculated recrystallization activation energy Qr was 145. 3 kJ/mol.