The present invention treats crushed pieces of a nonmetallic honeycomb panel together with a process water under high-temperature and high-pressure for a predetermined time so as to separate components. Water or alkali-added water is used as process water. The method comprises a first process for treating the crushed pieces for a predetermined time with the water heated and pressurized to a subcritical range to hydrolyze aromatic polyamide, and a second process for treating the same with the water heated and pressurized to a supercritical range, wherein the aromatic polyamide is hydrolyzed and separated in the first process, and dehalogenation is carried out in the second process.