Abstract: The effects of 600 ℃ tempering process on the microstructure and properties of V-N microalloy steels for offshore engineering were studied by XRD, SEM and TEM methods. The results show that with the prolongation of the tempering time, the Vickers hardness has a slight downward trend, the number of precipitated particles gradually increases,and the size of the precipitated phase increases. After 60 min of tempering, part of the martenite grains respond internally,dislocation movements cancel each other, only some of the grains have high-density dislocations, and the dislocation piling up is found at the grain boundary. With the tempering time reaches 120 min, the dislocation density in the martensitic slats is significantly reduced, and the phenomenon of entanglement disappears, which can form dislocation substructures within the martensite slat. After tempering for 240 min, the dislocation inside the martensitic slats basically disappears, and only a small number of dislocation products exist at the grain boundaries of the slats.