This paper deals with the bonding performance of phenol-formaldehyde (PF) resin in steam-injection heating at 160°C; the effects of additives and steam-injection time on bonding strength were studied. In addition, suitable bonding condition for PF resin in steam-injection heating was investigated. The results are summarized as follows: as steam-injection time increased, the bonding strengths of 3-ply plywood, glued with a neat PF resin and wheat flour extended PF resin after cyclic boiling treatment decreased. The reason seemed that swelling, dilution, and over-penetration of PF resin took place in long steam-injection heating. With sodium carbonate-added resin, the bonding strength increased gradually with increasing steam-injection time. To improve the bonding strength in a short heating time, intermittent steam-injection heating was tried. When a neat resin and sodium carbonate-added resin were used, the bonding strengths were improved dramatically. Therefore, intermittent steam-injection heating was effective for the development of the bonding strength of PF resin.