The invention relates to a method for preparing Ce0.8Gd0.2O1.9-Gd0.2Sr0.8FeO3-delta superfine powder through a one-pot precipitation method and belongs to the field of rare earth material preparation. Ce0.8Gd0.2O1.9-Gd0.2Sr0.8FeO3-delta is a mixed-conducting oxygen-permeable membrane material and has a wide application prospect in the field of oxygenerators, oxygen sensors, fuel batteries and synthetic gas catalysis. The method includes: preparing a mixed solution of CeCl3, GdCl3, SrCl2 and FeCl3 according to a stoichiometric ratio, and heating the mixed solution to 60 DEG C; adding PEG10000 and glacial acetic acid, and adding a Ce(NO3)4 solution into the mixed solution after PEG10000 is dissolved; adding an ammonium bicarbonate solution, and when pH value of precipitation mother liquor reaches 7, heating and boiling a precipitation system to obtain brown precipitate; filtering, washing and drying the precipitate, and calcining the precipitate at 900 DEG C to obtain 75wt.% Ce0.8Gd0.2O1.9-25wt.%Gd0.2Sr0.8FeO3-delta superfine powder which is high in dispersity and uniform in particle and 200-500 nm in median particle diameter D50 and has fluorite phase and perovskite phase.