Abstract: To explore the most suitable steaming process, Eucalyptus grandis × E.urophylla boards with thickness of 20 mm, whose moisture content of 130%, 60%, 50%, 30%, 20% were steamed at 80 ℃, 100 ℃, 120 ℃ respectively. Visible defects were investigated, combining with scanning electron microscope to analyze the micro structure before and after steaming. Changes of moisture content, the extractives content and defects developing during kiln-drying were considered. Results showed that the steaming effects were satisfactory when the MC was 50% and temperature was 100 ℃, respectively. The degree of visible defects of samples steamed in this condition was slighter than other groups, effectively avoiding subsequent drying defects developing. Some of the pit membranes in samples were broken up and ducts were smooth, contributing to improving the permeability. There was a slight reduction of hot water, 1% NaOH and benzene-alcohol extractives after steaming, which provided evidence that duct was clear and the permeability was improved.