Unsymmetrical dimethylhydrazine (UDMH) oxalate was synthesized using waste UDMH, and its structure was identified by element, FT-IR, ¹H NMR, DSC and UV analysis. The results show the melting point of UDMH oxalate is about 143-146 ℃ and its decomposition temperature is about 180.36 ℃. Its synthesis is simple, safe and efficient. Compared to liquid UDMH, solid UDMH oxalate has better thermal and aqueous solution stability and is easily stored, which is a new way to reuse the waste of UDMH.