The urea formaldehyde （UF） resin for plywood was modified with melamine and polyvinyl alcohol （PVA）. The effects of modified UF resin makings including final molar ratio, quantity of melamine, PVA and final temperature, and property indexes including viscosity, solid content and free formaldehyde content on prepressing intension of assembled mat were studied. Results showed that larger quantity melamine had no advantage of improving the prepressing intension, and PVA could help to increase original viscosity obviously, but the original viscosity could not determine the prepressing intension. The high temperatures of final reaction and short curing time were good for the prepressing intension, but prepressing intension decreased with solid content of resin increased. The low free formaldehyde content had little effect on prepressing intension.