The outdoor multi-channel antenna mainly contains a case, a reflection box, a reception plate, and a cover. The reflection box is placed inside the case. The reception plate has an antenna waveguide element and is placed inside the reflection box. The waveguide element is fixed and positioned by a support seat. The reception plate contains a curved piece and two wing pieces bended 90 degrees downward from the curved piece. The waveguide element is attached to a back side of the reception plate and is connected via a coaxial cable to a terminal threading through the through openings of the reflection box and the case. The cover tightly seals the case by a ring washer sandwiched therebetween and a waterproof plug sleeves over the terminal.