The invention discloses a support of a bridge portal pier top closure section and installation method of the support. The support comprises two standard section formwork arranged oppositely, two closure section side formworks correspondingly arranged on the two standard section formworks, one closure section top formwork arranged at the tops of the two closure section side formworks and at least one group of oblique supporting rods, wherein each group of the oblique supporting rods comprises a plurality of symmetrically distributed oblique supporting rods, the two ends of each oblique supporting rod are correspondingly connected with the standard section formworks and the closure section top formwork; and each group of oblique supporting rods is equipped with a group of traverse supportingrods closely adjacent to the group of the oblique supporting rods, each group of the traverse supporting rods comprises a plurality of traverse supporting rods distributed at intervals along the vertical plane, and the two ends of each traverse supporting rod are correspondingly connected with the two closure section side formworks. According to the bridge portal pier top closure section and installation method of the support, the multiple traverse supporting rods and the oblique supporting rods are adopted, construction load of the pier top closure section is decomposed into vertical force and horizontal force, and the vertical force and horizontal force are eventually transmitted to the standard section formworks and concrete on the standard section formworks, and the construction technology without embedding is realized.