TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): Compound (I) is prepared by (A) at - 20-35 degrees C, dripping 98 wt.% fuming nitric acid into acetic acid solution of 9,9'-dialkyl substituted fluorene compound of formula (II), where mol ratio of compound (II) and nitric acid is 1:1-50; reacting for 10 minutes-10 hours; and separating to obtain 2,3-nitro-9,9'-dialkyl substituted fluorene compound of formula (III); (B) adding alcohol solution of compound (III) into iron powder-hydrochloric acid reducing system, where mol ratio of iron powder to compound (III) is 2-30:1; reacting for 10 minutes-10 hours; thermally filtering to remove residual solid; cooling the filter liquid to precipitate solid; filtering; and washing the filter mass to obtain 2-amino-9,9'-dialkyl substituted fluorene compound of formula (IV); (C) dripping acetic anhydride into acetic acid solution of compound (IV), where mol ratio of compound (IV) and acetic anhydride is 1:1-30; at - 10-30 degrees C, reacting for 20 minutes-20 hours; adding water to stop the reaction to precipitate; reducing pressure and pump filtering; and separating the obtained solid to obtain 2-acetamide-9,9'-dialkyl substituted fluorene compound of formula (V); (D) at - 50-30 degrees C, dripping 98 wt.% fuming nitric acid into acetic acid solution of compound (V), where mol ratio of compound (V) and nitric acid is 1:1-40; reacting for 1 minute-2 hours; pouring the reaction liquid into water to precipitate; reducing pressure and pump filtering; and washing the filter mass with water to obtain 2-acetyl-3-nitro-9,9'-dialkyl substituted fluorene compound of formula (VI); (E) dissolving compound (VI) into 60-90 wt.% concentrated sulfuric acid; at 50-130 degrees C, hydrolyzing for 20 minutes-15 hours; adding water to precipitate; pump filtering; and washing to obtain 2-amino-3-nitro-9,9'-dialkyl substituted fluorene compound of formula (VII); and (F) adding alcohol solution of compound (VII) into iron powder-hydrochloric acid reducing system, where mol ratio of iron powder to compound (VII) is 2-30:1; at 50-150 degrees C, reacting for 5-10 minutes; and obtaining compound (I).