Global exploration of isomers and isomerization channels on the quantum chemical potential energy surface (PES) is performed for H3CNO3 using the Scaled Hypersphere Search-Anharmonic Downward Distortion Following (SHS-ADDF) method. The molecular formula of H3CNO3 includes functional groups of CH3, OH, NH2, COOH, NO, NO2, and NO3, which are very important in connection with amino acids and NOx. Geometrical structures and interconversion pathways are disclosed after 18719781 force calculations and 534726 Hessian calculations at the level of B3LYP/ 6-31G(d). The explored results are confirmed to be valid, especially for the important lower energy regions, by reoptimization at the higher level of B3LYP/ 6-31111G(d, p). A global reaction route-mapping using SHS-ADDF demonstrates the entire view and undeveloped landscapes on PES of H3CNO3. Typical compounds of H3CNO3, aminoxy formic acid, hydroxycarbamic acid, aminoperformic acid, hydroxymethyl nitrite, nitromethanol, methyl nitrate, methyl peroxynitrite, and dioxaziridine, are well separated from others by very high energy-barriers. The stable-most conformer of H3CNO3 is difficult to be determined, because of seven structures existing with nearly the same energies within 5.7 kJ/mol at the level of CCSD(T)/aug-cc-pVTZ. (C) 2017 Wiley Periodicals, Inc.