This invention discloses a method for preparing urea-formaldehyde resin, which is prepared from: formaldehyde 200 parts, urea 100-250 parts, poly (vinyl alcohol) 0.5-6 parts, accelerator 0.05-0.5 part, and additive 0.5-5 parts. The concentration of formaldehyde is higher than 42%. During the reaction process, urea is added in batches, so the raw materials react in strongly acidic, neutral to week alkaline, weak acidic and neutral media in sequence. The prepared urea-formaldehyde resin has a free formaldehyde content of only 0.05-0.20%. The production of artificial board, such as flake board and low/high density fiberboard, from the urea-formaldehyde resin has such advantages as no need for vacuum dehydration treatment, no wastewater discharge, short production period, and low fuel and energy consumption. The artificial board, when compared with that produced from low-concentration formaldehyde (37%), has such advantages as obviously improved physical and mechanical properties, and low free formaldehyde content.