Provided is a method for manufacturing a constructional panel with lightweight and incombustibility by filling a drawer type panel assembly with raw materials comprising expanded perlite and vermiculite. The incombustible panel is manufactured by the following steps of: crushing perlite and vermiculite into a 1-10mm size and sintering at 1000-1200deg.C to expand perlite and vermiculite; mixing expanded minerals with inorganic or organic binders such as latex, melamine and sodium silicate to obtain panel materials; filling a drawer type panel assembly, containing upper and lower sides with a distance of 50-150mm, and left and right sides made of steel, with mixtures, wherein the panel assembly is equipped with cores reinforcing steel to increase the strength of panel; heating the formed panel to 120-200deg.C for hardening and drying.