1,3,5,7,7-pentanitro-1,3,5-triazacycloactane and its intermediate 3,7,7-trinitro 1,3,5-triazabicyclo[3,3,1]nonane were synthesized. The mechanism of condensation reaction of methylenedinitramine, 2,2-dinitropropanediol-1,3 with hexamethylenetetramine is discussed herein.