The invention discloses a diffuser, a power system and a bladeless fan. The diffuser comprises a first part and a second part. The first part includes a first air guide cavity and a first wing arranged in the first air guide cavity. The second part is connected with the first part. The second part includes a second air guide cavity, and a second wing arranged in the second air guide cavity. A first positioning structure is formed at the first part; a second positioning structure is formed at the second part; and the first positioning part and the second positioning structure are matched for positioning to align the first wing and the second wing. In the diffuser, the first positioning structure and the second positioning structure can be matched to align the first wing and the second wing so as to guarantee the cyclone eliminating effect of the diffuser.