The method and assessment standard of munition in slow cook-off test is introduced and the factors affecting slow cook-off response of munition are analyzed. The characteristics of slow cook-off of HTPB/AP propellants at abroad are summarized. Results show the porous materials produced by thermal decomposition of ammonium perchlorate is the important factor causing HTPB/AP propellants to demonstrate violent reactions in slow cook-off test. Furthermore, the techniques to improve the slow cook-off response of AP based propellants are pointed out.