The square axial flow fan, abbreviated as DFBZ series fan, adopts a low-noise fan specific motor direct connection transmission; The whole machine is made into a square shape, with a beautiful appearance and convenient installation of reserved square holes on the wall; The air outlet is equipped with self hanging louvers to prevent outdoor rainwater and natural wind direction from backflowing indoors. It has obvious advantages such as firm installation, low vibration, low noise, and smooth operation, and is widely used for wall exhaust in industrial and mining enterprises, civil buildings, sports venues, animal husbandry, and various entertainment venues. The DFBZ-I model adopts an inner rotor motor direct transmission structure, the DFBZ-II model adopts an inner rotor motor and belt transmission structure, and the DFBZ-III model adopts an outer rotor motor direct transmission structure. It can be made into anti-corrosion and explosion-proof types according to user requirements.