The impurities of propanetiol dinitrate in nitroglycerin (NG)/dinitroglycol (TEGDN) were determinated by liquid chromatography photodiode array detection/electrospray ionization time of flight spectromass (HPLC-TOFMS), and the experimental conditions were as follows: Gemini5μC-18 (250 mm×4.6 mm,5 μm) column, mobile phase of 55% methanol and 45% water, and the negative mode of electrospray ion (ESI) source. Results show that the impurities is from NG, and are 1,3-propanetiol dinitrate and 1,2-propanetiol dinitrate. The deviation coefficient of variation for their quantities was 0.021% and 0.056%,respectively. The precision satisfy the application for distiguishing the content difference of propanetriol dinitrate in different NG/TEGDN.