The invention discloses a sanding dust screening device, and relates to the technical field of board processing. The device comprises a spiral dust conveyor and a dust conveying fan, wherein a screening air box is connected to a discharging port of the spiral dust conveyor; the screening air box is connected to the dust conveying fan through a pipeline; a first screening object outlet is formed inthe bottom part of the screening air box; an air inlet is formed in the upper part of the first screening object outlet, and an air inlet adjusting plate is mounted; a dust scattering device is mounted at the discharging port of the spiral dust conveyor; a plurality of flow guide adjusting plates which are vertically arranged at intervals are mounted in the screening air box; and a plurality of second screening object outlets are formed in the lower parts of the flow guide adjusting plates. Compared with the prior art, the device has the advantages that sanding dust is scattered into dispersed dust through the scattering device and is screened by layers through the plurality of flow guide adjusting plates; sand and large dust particles are screened out; the screening effect is good; the recovered sanding dust basically does not contain sand; and when a rough board is subjected to sanding, the surface is prevented from sand marks.