A series of polystyrene-supported 1-(propyl-3-sulfonate)-3-methyl-imidazolium hydrosulfate acidic ionic liquid (PS-$[SO_3H-PMIM][HSO_4]$) catalysts were prepared and tested for mononitration of simple aromatics compounds with nitric acid. It was found that the reactivity of the catalysts increased with increasing $[SO_3H-PMIM][HSO_4]$ content. The para-selectivity was not only related to the $[SO_3H-PMIM][HSO_4]$ content but also the substituent groups in aromatics. A reaction mechanism of nitration over this new catalyst was proposed. The catalytic activity of this catalyst decreased slightly after fifth runs in the synthesis of nitrotoluene.