The invention discloses a deorbiting device for a micro / nano satellite. The deorbiting device for the micro / nano satellite comprises a sail storing device, a sail unfolding device and an unlocking device, wherein the sail unfolding device is of a centrosymmetric structure, and comprises an upper end cover, a lower end cover, a clack-shaped central shaft, two ring flanges, two strip elastic masts, four supporting prisms, four pairs of pilot sleeves, four hold-down mechanisms and four leaf springs. After a ground command is received, the unlocking device releases the clack-shaped central shaft of the sail unfolding device; the strip elastic masts wound on the clack-shaped central shaft drive a thin-film sail, which is stored in a sail storing chamber, to unfold through releasing elastic potential energy stored by the strip elastic masts. According to the deorbiting device for the micro / nano satellite, the normal sectional area, in which a satellite moves, is increased by utilizing the unfolding of the thin-film sail, the effect of atmospheric drag perturbation on the micro / nano satellite is enhanced, and thus, the passive deorbiting of the micro / nano satellite is prompted.