A film sample of aromatic polyamide, or so-called Aramid, was subjected to grinding in air with calcium oxide (CaO) powder by using a planetary ball mill, to investigate its mechanochemical decomposition. The reaction was found to proceed with an increase in the period of grinding time, and all chlorine in the film was transformed into inorganic chlorides in prolonged grinding. The process was characterized by X-ray diffraction analysis, thermogravimetric analysis, scanning electron microscopic observation, and Raman shift analysis. The main products after decomposition reaction were water-soluble calcium chloride hydrate, amorphous carbon, calcium carbonate, and a small part of calcium nitrite, as a result of a rupture in the covalent bonds of C - C, C - Cl, C-N, and C-H in aramid film construction into some new bondings. The most significant phenomenon was the formation of Ca(NO2)(2), suggesting the strong oxidative ability of CaO during the mechanochemical reaction.