The invention discloses a device for preparing nanoscale antimony trioxide. The device comprises an antimony white furnace and a reactor and is characterized in that a front chamber, a middle chamber and a rear chamber communicated with one another are arranged in an inner chamber of the antimony white furnace, a rotary air blower is arranged at the top of the front chamber, a bottom blowpipe and a top blowpipe are arranged in the middle chamber, the bottom blowpipe extends into antimony liquid, the top of the rear chamber is connected to the reactor, and a double-layer crystallizer is arranged at the top of the reactor.