The invention discloses a composite material tower reinforcing device. The composite material tower reinforcing device comprises a first sectional material and a second sectional material, wherein the right-angled section of a composite sectional material is coated with the first sectional material with an L-shaped cross section, the arc-shaped section of the composite sectional material is coated with the second sectional material with an arc-shaped cross section, and the first sectional material is connected with the second sectional material through a fastener. An installation method includes the following steps that the reinforcing device with an appropriate length is fetched, and the inner surface of the first sectional material and the inner surface of the second sectional material are evenly painted with resin adhesives and then bonded to the right-angled section and the arc-shaped section of the middle of the composite sectional material needing reinforcing; after the resin adhesives are solidified, the first sectional material and the second sectional material are tied together through the fastener. The composite material tower reinforcing device has the advantages that a weak rod piece in a composite material tower can be reinforced by the reinforcing device, so crack generation and expansion caused by stress concentration or large deformation are prevented, the rod piece can be protected against large deformation, the bearing capacity of the composite material tower is improved, and the capacity of the tower to resist natural disasters is enhanced.