The invention discloses a synthesizing method of deuterated octogen. The synthesizing method is characterized by comprising the following steps of enabling a deuterated formaldehyde matter and an ammonia compound to react, so as to obtain an intermediate, namely deuterated urotropine; further acetylizing and nitrifying, so as to obtain an intermediate, namely 1,5-diacetyl-3,7-binitro-1,3,5,7-teraazamacrocycle octane; using nitric acid/phosphorus pentoxide to nitrify, so as to obtain the product with high selectivity, namely deuterated octogen. The deuterated octogen synthesized by the method has the advantages that the purity is high, the deuterating rate is high, and the deuterated octogen can be applied to the fields of neutron diffraction, energetic material study, analysis and detection, and the like.