The invention discloses a lightweight lath for a building. The lightweight lath comprises a paint spraying layer, a straw plate, a cement pressure plate and a polystyrene foamed plate; the paint spraying layer is located on the outer surface of the straw plate; the cement pressure plate is arranged between the straw plate and the polystyrene foamed plate; and the straw plate is prepared from the following raw materials in parts by weight: 99-136 parts of plant straws, 38-56 parts of water glass, 15-18 parts of hemp cut lime, 8-10 parts of discarded toughened glass micropowder and 7-9 parts ofbeidellite. The cement pressure plate is prepared from the following raw materials in parts by weight: 80-93 parts of spherical quartz powder, 120-133 parts of cement, 60-75 parts of white clay, 40-65parts of pearlife, 30-45 parts of sepiolite amiantus and 20-32 parts of paper strips mixed lime mortar; and the polystyrene foamed plate is prepared from the following raw materials in parts by weight: 20-40 parts of polystyrene, 7-13 parts of chorion powder, 25-40 parts of dacron pulp, 7-12 parts of nanometer zirconium silicate, 1-2 parts of diisopropyl azodicarboxylate, 1-2 parts of p-toluenesulfonyl semicarbazide and 1-3 parts of methylene bis-benzotriazolyl tetramethylbutylphenol. The lightweight lath disclosed by the invention is excellent in overall performance.