A beam scanning antenna, a microwave system, and a beam alignment method are disclosed. The method includes: instructing, by a switching control module, a feed switching module to enable each feed in a multi-feed antenna, so that the feeds separately perform signal quality detection, where the multi-feed antenna includes an aperture unit and at least two feeds, where the feeds are configured to radiate an electromagnetic wave signal, the feed switching module includes multiple switches, and each feed is respectively connected to one switch in the feed switching module; acquiring, by the switching control module, a result of the signal quality detection performed by each feed; and selecting, by the switching control module according to the result of the signal quality detection, one feed having the best signal quality as a working feed.