Abstract: Formaldehyde methyl hydrazine, the secondary reaction product of MMH in DMHAN-MMH solution was detected and verificated by gas chromatographymass spectrometry（GC-MS） in this research. DMHAN-MMH nitrate solution stored for a long time will be changed yellow. The main reason is that part of MMH is oxidized to be HCHO by oxygen in the air, and then HCHO and MMH is to be methyl hydrazone by condensation reaction. Low temperature, closed environment and dark is conducive to the preservation of DMHAN-MMH nitric acid solution. At room temperature, 10^-3 mol/L MMH has no significant effect on the stripping ratio of macroconcentration Pu(Ⅳ) in 30%TBP-dodecyl hydride, but it has obvious effect on the stripping ratio effect of low concentration of Pu(Ⅳ) (<0.5 g/L) and the lower the concentration of plutonium, the more obvious the effect.