The invention discloses a temporary support method for a modular adjustable posture for prefabricated cover beam installation. The method comprises the steps of arranging a section steel support platform directly below a preset lifting position of each prefabricated cover beam, and arranging a connecting rail in the bridge direction between the adjacent section steel support platforms; arranging atop plate movable in the bridge on the top surface of the section steel support platform, and mounting a support assembly vertically fixedly on the top surface of the top plate to make the support assembly support the first prefabricated cover beam; after the first prefabricated cover beam is hoisted and positioned, moving and fixing the top plate and the support assembly thereon along the connecting rail to the section steel support platform below the second prefabricated cover beam to make the support assembly support the second prefabricated cover beam; repeating the above steps until thehoisting and positioning of all the prefabricated cover beams are completed. The method has the advantages that the top plate and the support assembly can be moved between the adjacent section steel support platforms, and the cumbersome steps that the support assembly needs to be removed and hoisted are eliminated, thereby accelerating the construction efficiency.