The new nanosolid superacid Fe₂O₃／SO₄^2- was prepared by using nanometer chemical technology. Samples were characterized by XRD and TEM. The results show that Fe₂O₃／SO₄^2- is superfine solid belonging to nanocrystal and its average size is 40 nm with good distribution. The regioselection and activity of chlorobenzene nitration was raised,when the nanosolid superacid Fe₂O₃／SO₄^2- was taken as the catalyst. The optimum reaction conditions were found out. Thus activated temperature of catalyst was 600 ℃，the reaction was carried out at 50 ℃ for 6 h with n(nitric acid)／n(chlorobenzene) equalling to 3.5 and m(chlorobenzene)／m(catalyst) equalling to 20 to get the yield of 78.7%,the ratio between para- and ortho-mononitrochlorobenzene(P／O) reaching up to 4.8.