A new generation of building decoration board is made by using magnesium oxychloride as the core material, galvanized or color coated board as the surface layer (two layers), and high-strength adhesive. It is heated and pressed by a high-speed continuous automated forming machine, and then trimmed, slotted, and cut. The hydrophobicity of magnesium oxychloride color steel sandwich panel is greater than 98%, and it does not deform or react chemically when in contact with water. The sandwich panel has high strength and can reach a length of 10m, with good insulation and sound insulation effects.