TATB-based PBX samples with different densities were prepared by different press process, and their position lifetime spectra were measured. The spectra show that the positronium formation is negligible in TATB-based PBX, therefore the 2-component fit is applicable. The result shows an increasing dimension but decreasing concentration of nano-void during PBX pressing,which means the nano-void in TATB crystalline increased due to the damage and crack under pressure, however the nano-void of intergranular interface decreased.