For investigating the ignition mechanism of HTPB propellant under waterjet high pressure，Hartman bomb was used to study the lower limit of explosion density and the minimum ignition energy of the AP/HTPB/ferrocene system，and the effects of AP content，ferrocene content and ambient humidity on the characteristics of dust explosion were analyzed. Results show that with the increasing of AP and ferrocene content，the minimum ignition energy and the lower limit of dust explosion density of the mixed system decrease; with the increasing of ambient humidity (80%-90%)，the minimum ignition energy and the lower limit of explosion density of the mixed system containing ferrocene change gently.