The invention discloses a microwave antenna and an outer cover thereof. The outer cover is a rotational symmetric element which comprises a plurality of homocentrically arranged parts as below: a compensation part arranged at the middle of the outer cover and used for compensating the phase delay of the electric field distribution at the middle of an antenna aperture surface caused by the shielding of a feed source, a main reflection part arranged at the periphery of the compensation part and used for reflecting the electromagnetic wave emitted from the microwave antenna feed source to a specific direction deviating from the feed source, and an assistant reflection part arranged at the periphery of the main reflection part and used for carrying out reflex bunching on the edge diffraction electromagnetic wave of the microwave antenna. All the parts of the outer cover are especially designed and shaped, therefore the microwave antenna has the characteristics of excellent electrical properties, stable structure, low cost and the like.