In order to study the low-pressure heat treatment on density and inner quality of pressed PBX, pressed PBX specimens were treated in isostatic pressing machine with pressure range of 5-10 MPa for 2-4 hours and repeated for 1-3 times. The properties of pressed PBX before and after treatment were compared. Results show that low-pressure heat treatment releases internal stress, increases relative density of PBX from 96.53%-98.83% to more than 99%, improves inner quality, and restrains growth of pressed PBX charges.