In order to understand the combustion and explosion mechanisms of energetic materials, the cracking pathways of 2,4,6-trinitrophenol(PA) and 2,4,6-trinitroresorcin(H₂TNR) were studied by electric spray ionization mass spectrometry(ESI-MS), and their cracking mechanisms were analyzed. Results show that cracking modes of the two compounds were loss of NO₂,OH,O,NO,CO,CNO and CNO₂, and those with a hydroxy group ortho to the nitro group exhibit predominant “ortho effect”, and the facile transfer of a hydroxy hydrogen to oxygen followed by loss of OH. When the number of nitro groups is definite, “ortho effect” becomes more important with increasing of the number of the ortho hydroxy groups,and the compounds are more easily to lose OH rather than lose NO₂ firstly.