To study the chemical structure of the HMX flame, species and temperature profiles were measured in the gas phase at heat fluxes of 100 and 300 W/cm(2). A microprobe/triple quadrupole mass spectrometer was used to measure quantitative species profiles, and fine wire thermocouples were used to measure temperature profiles. The flame and surface structures were observed using a high-magnification video system. The major species at the surface were H2O, CH2O, HCN, NO2. N2O, N-2. CO, and NO at atmospheric pressure with both heat fluxes. There was no CO2 existing at the surface. The mole fraction of triazine was found to be approximately 2.5% at the surface, which has not been reported during combustion of HMX. The species could play an important role in the gas phase chemistry. The species profiles showed two-stage reaction zones. The species profiles also showed that increasing heat flux stretched the secondary reaction zone, but did not stretch the primary reaction zone. No plateau at a typical dark zone temperature was observed for either heat flux. Finally, the temperature profiles in the gas phase and species concentrations obtained at the surface with heat fluxes of 100 and 300 W/cm(2) were used as inputs to a 1-D gas-phase flame model. Disagreement between the model and experiments for stable species was observed and investigated in detail.