The invention discloses a method for preparing lightweight aggregate concrete. The method comprises the following steps: wetting the surface of lightweight aggregate, mixing a cementing material withthe lightweight aggregate in a coating manner to form a thin layer of a cementing material slurry on the surface of the aggregate, performing uniform mixing, ram-molding the obtained mixture in a moldto form macro-porous sandless lightweight concrete, allowing the macro-porous sandless lightweight concrete to become hard in order to prepare a high-fluidity mortar, filling the macro-porous sandless lightweight concrete with the high-fluidity mortar, and vibrating and exhausting the circumference of the mold to finally obtain lightweight aggregate concrete. The lightweight aggregate is integrally connected through a small amount of the cementing material slurry to form the macro-porous sandless lightweight aggregate concrete, and then the high-fluidity mortar is injected to permeate the gapgaps in the lightweight aggregate, and the cementing material in the lightweight aggregate is solidified and molded to make the lightweight aggregate not float upwards, so the technical problem of upward floatation of ceramsite in the lightweight aggregate concrete is completely solved.