The invention discloses a construction method for the heat-insulating wall body of a building. The method adopts the combined system of an inner wall heat-insulating decorative material and an outer wall heat-insulating decorative material for the wall body of the building, and comprises the following steps: plastering phase-change energy-storage inorganic/organic heat-insulating mortar, plastering phase-change energy-storage rendering mortar and mesh fabric, puttying phase-change energy-storage flexible water-fast putty, coating permeating-type elastic priming paint through rolling, and coating solar reflection heat-proof exterior wall coating through rolling on the outer wall of the wall body; plastering phase-change energy-storage desulphurized gypsum heat-insulating mortar, puttying temperature-regulating humidifying anti-bacterial flexible putty, and puttying temperature-regulating humidifying anti-bacterial interior wall coating on the inner wall of the wall body; and the like. Through the adoption of the construction method, the wall body has the functions of heat insulation, energy conservation, air purification, solar phase-change temperature adjustment, moisture absorption, moisture discharging, sound absorption, noise reduction, bacterium resistance, mold prevention, water prevention, and ventilation. Therefore, the method has the advantage that the functions of low carbon emission, pollution reduction, energy conservation, beautiful decoration and environment protection of the wall body are realized; and the method is convenient to popularize and apply.