The invention relates to a light energy-saving seam split-preventing wallboard, wherein the upper mounting plate and the lower mounting plate and both side butt-joint edges of the wallboard are provided with grooves used for butt joint; the surface layer of the wallboard consists of a slurry layer and more than one layer of fabric layer; the fabric layer extends out of a face plate to form a mounting lapping conglutination layer; the slurry layer is prepared from raw materials according to the following part by weight: 30 to 40 portions of magnesium sulphate or magnesium chloride, 80 to 100 portions of magnesium oxide, 30 to 50 portions of coal ash, 50 to 60 portions of scrap plant fiber, 10 to 15 staple glass fiber, 0.6 to 1 portions of modifier and 120 to 160 portions of water. The wallboard which has reasonable structural design can greatly increase the cohesive force of the wallboard during butt joint; meanwhile, when installed through adopting the method of the invention, the wallboard can completely eliminate the seam split phenomenon of a wall body during use. Moreover, the wallboard has the advantages of light weight, high strength, no crushing and good thermal-insulation effect and good inflaming retarding effect, etc.