NOVELTY - Preparing calcium ferric oxide nano powder, comprises: (i) preparing calcium nitrate solution and ferric nitrate solution, (ii) adding ferric nitrate solution into calcium nitrate solution, and uniformly mixing to obtain mixed solution A, (iii) adding glycine into the mixed solution A, and stirring uniformly to obtain mixed solution B, and (iv) heating the mixed solution B in a muffle furnace to 100-300 degrees C and insulating to obtain primary dark brown fluffy powder, and then roasting the primary powder in the muffle furnace to 300-700 degrees C.    USE - The nano powder is used as a photocatalyst for degrading organic pollutants or as a cathode material for solid fuel cells.    ADVANTAGE - The method uses cheaper raw materials and has simple technological operation; lowers the roasting temperature, thus being beneficial to energy saving and environmental protection; and uses glycine as a combustion improver, and is non-toxic and harmless, thus ensuring the health and safety of operating personnel. The nano powder has high purity, small and uniform particle size and favorable crystallinity.    DETAILED DESCRIPTION - Preparing calcium ferric oxide nano powder, comprises: (i) respectively preparing analytically pure ferric nitrate and analytically pure calcium nitrate into 0.1-1 mol/l calcium nitrate solution and 0.1-1 mol/l ferric nitrate solution, (ii) adding ferric nitrate solution into calcium nitrate solution, and uniformly mixing to obtain mixed solution A, in which the mol ratio of iron ion and calcium ion is 1:1, (iii) adding glycine into the mixed solution A, and stirring uniformly to obtain mixed solution B, where, the adding amount of glycine is 1-3 times the total molar amount of ferric nitrate and calcium nitrate in the mixed solution A, and (iv) heating the mixed solution B in a muffle furnace to 100-300 degrees C and insulating to obtain primary dark brown fluffy powder, and then roasting the primary powder in the muffle furnace to 300-700 degrees C.