The invention relates to an assembly-type horizontal splicing light and thin template and a construction method thereof, and belongs to the technical field of assembly-type constructions. The assembly-type horizontal splicing light and thin template comprises a horizontal straight segment template and a corner segment template; two parallel light and thin panels and a plurality of tying rods are connected to form the horizontal straight segment template, the tying rods are arranged between the two light and thin panels, thereby playing roles of connection and reinforcement, and the upper and lower end portions of the horizontal straight segment template are respectively provided with feature clamping strips; two mutually perpendicular light and thin panels and two mutually perpendicular stiffened thin plates are connected to form the corner segment template, a plurality of holes are formed in the stiffened thin plates, and the end portion of the corner segment template is provided witha clamping strip. The template can effectively save timber resources and labor cost, the hoisting cost is canceled, the construction period is shortened, the building industrialization degree is improved, and the building assembly rate on the site is improved.