The utility model discloses a template supporting device for a diaphragm plate of a T-shaped beam bridge floor system. The problems that the template supporting device is easily damaged and the repeating utilization factor of the template supporting device is low in the traditional template supporting technology of the diaphragm plate in erection of a dual-line T-shaped bridge are solved. The template supporting device comprises a front lateral template (19), a rear lateral template and a bottom template (18) which are respectively arranged on a diaphragm seam (5), wherein a front underpinning steel angle and a rear underpinning steel angle are respectively arranged on the bottom surfaces of the front and rear sides of the bottom template (18); hanging holes are formed in the underpinning steel angles; crossed hooks are connected with the underpinning steel angles through tighteners in a hooking manner; two hanging holes are also respectively formed in the left and right ends of the underpinning steel angles, and connected with tips of embedded bars of two T-shaped bridges in a wet joint (6) through the hooks and the tighteners respectively in the hooking manner. By adopting the template supporting device disclosed by the utility model, no support rack is arranged on the bridge floor, so that the bridge floor is prevented from being crushed and damaged by vehicles; the repeating utilization factor of the templates is high; and the construction efficiency is improved.