Trinitroethyl-N-nitromethylamine(TNEMA) is well known as a powerful nitramine and was studied widely in the 1960′s. We have studied a sample TNENA stored for 35 years and want to estimate the change of its properties after a long term storage.For this aim,the chemical structure of TNEMA has been determined by IR,¹HNMR,MS determination and elemental analysis. The obtained results are as follows: compared with the new synthesis sample,there are two new peaks (2 000 MHz,CDCl₃,ppm): 3.549(s,3H,CH₃),5.267(s,2H，CH₂) in ¹HNMR spectrogram for 35-year stored TNEMA,which is similar to those of TNEMA stored for 11 years.MS data demonstrate that both 11-year stored and 35-year stored TNEMA have the same molecular-ion peak and main fragmental peak as the new synthesized sample. And elemental analysis show the same CHN content for long storge and new synthesized sample.The study of thermal decomposition of TNEMA samples demonstrates that the apparent activation energy of thermal decomposition is of the same order for storage and new synthesized samples. A determination of impact sensitivity of samples with the help of Kast hammer gives next result: percent of explosion is 58%,64%,60% respectively for the samples of a new synthesis,17-year and 35-year storage.Basing on the data described above,we can obtain the conclusion that TNEMA is a quite thermally stable nitramine,because its chemical structure and kinetic parameters have not changed after a long term storage.