An umbrella comprises a cover and two rod hinges. A canopy is engaged with a rectangular frame for forming a rectangular cover. A left rainproof folding fan and a right rainproof folding fan, each has a pivot at a bottom linked with the bearings of the rectangular frame, respectively. Two sets of Velcro is linked with the rectangular cover, the left rainproof folding fan and the right rainproof folding fan for forming the cover. The two rod hinges is linked with the rectangular frame and attached onto two straps of a backpack through two fasteners, the each rod hinge having a bracket and a rod with a stopper and an outlet connected with the each pin respectively, wherein the cover and the two rod hinges form an umbrella with adjustable coverage which has the rectangular frame fixed with the stoppers when the cover is extended and the two rod hinges are extended and erected.