Abstract: The microstructure transfers were monitored by the expansion tests at the different cooling rates. By using the Gleeble-2000 thermal simulation machine, the impact toughness and the microstructures for the HAZ were also simulated. Furthermore, the weldments were performed to testify the consistency of the simulation specimen and the weldments. The results manifest that with the cooling velocity decreased, the Bainite transfer, the proeutectoid ferrite transfer, and proeutectoid ferrite pearite transfer take place in sequence. Accordingly the mechanical properties decreased. Under the condition of the multipass welds, the HAZ microstructures of the weldments consist of the mixed microstructure, but the base microstructures are same to that of the thermal simulations at the same cooing rate. The research results have a good direction and references to the welding fabrication.