The invention discloses a porous long-span simply-supported steel truss girder bridge erecting method. The erecting method includes: arranging flexible brackets on two sides of a bearing table along the bridge, wherein the flexible brackets include supporting beams extending upward from the bearing table and connection beams for connecting the supporting beams and a pile body; arranging a steel truss girder on each of the two sides of the pile body with the pile body and the supporting beams on the two sides of the pile body as supports, arranging a temporary rod between the two steel truss girders with the pile body and the supporting beams on the two sides of the pile body as the supports so as to connect the two steel truss girders; arranging steel truss girders on left and right sidesof the two steel truss girders further, and completing simply-supported steel truss girder bridge erecting. The dual-suspension arm symmetrical erecting method is adopted, most loads are transmitted to the bearing table during suspension arm construction through the pile body according to rigidity allocation between the flexible brackets and the pile body; the length of the steel girder suspensionarms can be shortened, deformation of a front suspension arm is reduced, ballasting and anchoring of a back end can be avoided, influence of geological conditions outside a bridge can be avoided, thenumber of construction supports can be reduced, on-site construction is convenient, the cost can be effectively controlled, and the safe risk is low.