The invention discloses an iron nail collecting device for a building construction site. The iron nail collecting device for the building construction site comprises a base, a pulley, an open pore, afixed vertical rod, an upper fixed block, a lower fixed block, a first motor, a screw rod, a movable block, a first electromagnet, a first spring, a metal block, a movable vertical rod, a housing, a rotary shaft, a big gear, a first permanent magnet, a second motor, a motor connecting rod, a small gear and the like. The iron nail collecting device for the building construction site provided by theinvention has the advantages of reasonable and simple structure, low production cost and convenience in installation, and can be used for effectively collecting iron nails on the building construction site and separating impurities in the iron nails so as to overcome the defects in the background technology; a pressing device is arranged for pressing the ground after the iron nails are collected,so that an uneven ground caused after the iron nails on the ground are collected is prevented; and after the iron nails are collected, the impurities contained in the iron nails can be effectively filtered so as to be removed, and the iron nails can be ensured to be directly used for the second time.