In a method of laying out abnormally-shaped grid decks, the abnormally-shaped grid decks refer to grid decks having a cut-out at the corner thereof. It is usually a problem when laying out abnormally-shaped grid decks because they will be off-balance when they are laid on the columns. Support frames are used to support the abnormally-shaped grid decks and keep them balanced and stable on the columns. However, the support frames may obstruct the working route used in construction. The method adopted in the present invention adds temporary beams to maintain the abnormally-shaped grid decks by balancing them on the columns before they are fixed and secured thereon, and thereafter the temporary beams will be removed. This method can prevent using support frames which may obstruct the working route under construction.