A construction method for a column platform barrel deck and topside facilities, and a column platform. The construction method includes: prefabricating topside facilities in form of modules one by one, lifting each module to a predetermined position on the topmost deck of the upright barrel, and then connecting the modules to each other and forming a module-integration bottom deck at the bottom; during construction of the upright barrel, a skylight opening is reserved on the barrel topmost deck for the installation of the topsides, and the skylight opening allows the modular-integration bottom deck to be placed inside; an on-site closing gap is formed between the edge of the skylight opening and the outer edge of the modular-integration bottom deck perimeter; using the on-site closing gap connection structures to fill the on-site closing gap, so that the modular-integration bottom deck and the barrel topmost deck jointly form an integrated platform deck.