The invention discloses an iron-based powder collecting device comprising an adsorption chamber, a first purging chamber and a slidable spiral casing grid, wherein the adsorption chamber is connectedto the first purging chamber; a plurality of magnet bars are evenly arranged in the adsorption chamber, a feeding port is opened at one end of the adsorption chamber, and a discharging port is openedat the opposite end of the feeding port; first compressed air nozzles corresponding to the magnet bars are evenly disposed in the first purging chamber, and the first compressed air nozzles are connected to one ends of the magnet bars; the slidable spiral casing grid comprises a movable vertical partition with through holes corresponding to the magnet rods and a spiral sleeve, the movable verticalpartition is connected to the spiral sleeve, and the spiral sleeve is sleeved on the magnet rods or the first compressed air nozzles and slides with the movable vertical partition on the magnet rodsand the first compressed air nozzles. The device has very simple structure and high removal efficiency, and the compressed air is used to clean the adsorbed iron-based powder, which can greatly save the operation intensity, and is low in cost and favorable for promotion.