The flame structure and reaction zone size of the dimethyl ether/air premixed flame in a cylindrical furnace were experimentally and numerically investigated in this paper. Seven cases of flames with different operational parameters were involved to reveal the influences of excess air ratio and thermal load on the combustion behaviors. The simulations were conducted using the eddy dissipation concept (EDC) model with a reduced chemical kinetic mechanism including 39 species and 168 reversible reactions. The present work demonstrated that the fluid structure in the furnace consisted of the flame core area (FCA), recirculation zone I (RZ I), and recirculation zone II (RZ II). In addition, the fluid structure was coupled with heat and mass transfer phenomena in the furnace and had a considerable effect on them. The temperature in the FCA was mainly dependent on the excess air ratio. The temperature in RZ II was strongly affected by the thermal load. Moreover, the temperature at the furnace outlet was positively correlated with the thermal load. The species contents in the overall furnace were mainly dependent on the excess air ratio. The influence of the thermal load over the species contents was rather insignificant. Moreover, the intensified diffusion outside the flame zone resulting from the decrement of temperature could change the species distributions in part. Research on the reaction zone size indicated that either the decrease of excess air ratio or the increase of thermal load could result in an enlargement of the reaction zone. Additionally, the mean reaction rate of the dimethyl ether/air premixed flame was found to be independent of the thermal load. It was observed to be dependent on the excess air ratio. Finally, a functional expression between the mean reaction rate and the excess air ratio was developed in this paper.