The invention discloses a concrete floor falling lower-plate hanging-template template system capable of high-quality demoulding and a supporting and dismounting method of the concrete floor lower-plate hanging-template template system. The problem that edges and corners of a lower plate are prone to being lack of and fallen in an existing lower-plate hanging-template template system is solved. The concrete floor falling lower-plate hanging-template template system comprises a left front L-shaped square steel template (1), a left rear L-shaped square steel template (2), a right front L-shapedsquare steel template (3) and a right rear L-shaped square steel template (4), wherein the four L-shaped square steel templates are spliced end to end to form a concentric-square shape, the end to endsplicing of the two L-shaped square steel templates are but joint together in a wedge-shaped surface form, and the formed four wedge-shaped splicing surfaces are spatially arranged in parallel with each other; fixing and connecting plates (10) are arranged at the splicing positions at which the two L-shaped square steel templates are connected end to end; a square steel diagonal brace (5) is fixedly arranged between the two inner sides of each L-shaped square steel template. The occurrence of missing edges and falling corners is avoided to the greatest extent when the templates are removed.