In the HTPB/Boron simple system and the HTPB propellant composed of total solid loading 70～75wt% containing modified boron powder B_S 40～35wt%，the effects of modified boron and the processing characteristics of propellant filled boron powder B_S were studied by means of yield value and apparent viscosity measured with HAAKE RV20 M5/SV2LF and M5/SV2 systems. The results show that according to the processing stability，BS is the best one of all the modified products including B_D、B_W、B_T and B_S. The propellants filled B_S exhibit a good castability,flow level and long potlife，and after mixing 2~3 h the slurry can be described with Casson or Bingham model，when shear up and down to stationary it exhibited obvious shear-thining and constraction recovery respectively.