The invention provides a lightweight high-strength high-ductility mortar and a preparation method thereof. The mortar comprises cement, silica fume, slag powder, recycled powder, fly ash floating beads, glass microbeads, recycled rubber powder, a water reducing agent, water, ultrahigh-molecular-weight polyethylene fibers and polyester fibers. The preparation method comprises the following steps of: mixing the cement, the silica fume, the slag powder, the recycled powder, the fly ash floating beads, the glass microbeads and the recycled rubber powder under stirring to obtain a first mixture; adding the mixed liquid of the water reducing agent and the water into the first mixture and carrying out stirring to obtain a second mixture; adding the ultrahigh-molecular-weight polyethylene fibers and the polyester fibers into the second mixture and carrying out stirring to obtain a third mixture; and finally, subjecting the third mixture to vibration molding and maintenance. The mortar of the invention has the characteristics of light weight, high compressive strength, high tensile strength, excellent energy-dissipating capacity, high stretching charge mass ratio and ultra-high tensile ductility, thereby significantly reducing the deadweight of materials and structures and maintaining sufficient bearing capacity.