The synthesis of 3-amino-4-amidoximinofurazan from malononitrile (MN) was proposed in the literature as four-step reaction: nitrosation, rearrangement, oximation and dehydration cyclization. In this paper the nitrosation was tracked via in situ IR, and 2-nitrosomalonitrile (NMN) and 2-oximinomalonitrile (OMN) (as a pair of isomer) were detected. In addition, the 3-demensional in situ IR spectra of —NO、 NOH and —OH, and the intensity history of characteristic peaks for —NO,CN and —OH during the nitrosation process were recorded and derived, which gives an insight into the nitrosation. But OMN was not successfully separated. As a product of reaction of MN with NaNO₂ and that of reaction of sodium salt of OMN (NaOMN) with NH₂OH, both of NaOMN and 1,3-diamino-1,2,3-trioximinopropane were obtained and characterized by IR, NMR, MS and elemental analysis. Based on what described above, we propose the following five-step mechanism for the title reaction: nitrosation, rearrangement, salification, oximation, and dehydration cyclization.