The invention relates to a full-assembly magnetic-attracted steel-concrete composite floorslab and an assembling method thereof. The floorslab is composed of a prefabricated concrete panel and a steelplate which are sequentially arranged from top to bottom, an inverted T-shaped permanent magnet is arranged on the prefabricated concrete panel, and the lower end of the inverted T-shaped permanent magnet is a magnetic-attracting receiving end; the steel plate is provided with a magnetic surface seat, a guiding groove is formed in the top of the magnetic surface seat, and the magnetic-attractingreceiving end is embedded in the guiding groove. The method comprises the steps that the magnetic surface seat is fixedly installed at a preset position of the steel plate, a magnet in the magnetic surface seat is rotated to reach a releasing state to stably place the concrete panel on the steel plate, the magnet in the rotary magnetic surface seat is rotated to reach an absorbing state to allow the concrete panel to be tightly absorbed on the steel plate through the magnetic attracting effect of the inverted T-shaped permanent magnet and the magnetic surface seat. By means of the full-assembly magnetic-attracted steel-concrete composite floorslab and the assembling method thereof, the construction efficiency can be effectively improved, and the problems of easy cracking and corrosion of asteel-concrete interface are solved.