The relationship between loading pressure and charge density is the fundamental parameters for micro-charges. It is very important to study and design the charge density,loading explosive weight,and detonation characteristics in micro-electro-mechanical systems (MEMS) fuzes. The relationships between loading pressure and loading density by volumetric method for two primer explosive lead azide carboxymethyl cellulose (CMC-Pb(N₃)₂) charges (micro-charge with internal diameter 0.9 mm and normal charge with internal diameter 5.28 mm) were studied. The fitting equations and relationship curves for the two charges were obtained,and the relationships between porosity and stress were got too.