With acetylacetone and hydrazine hydrate as primary substances, 1H,4H-3,6-dinitropyrazolo［4,3-C］ pyrazole(DNPP) was synthesized by the process of dehydration and condensation,the first nitration,reduction,diazotisation,intramolecular cyclic condensation,the second nitration,oxidation,decarboxylation and nitration in turn. The overall yield of DNPP was 9.3%. Its structure was confirmed by IR,¹H NMR, ¹³C NMR and elemental analysis. The mechanism of intramolecular cyclization reaction was presented. The results provide academic and experimental basis for the further research on the pyrazolo［4,3-C］pyrazole explosives.