Diethyl ether is widely used in the fields of diesel engines, agriculture, food, chemical, biological, pharmaceutical, and medical industries. It is necessary to carry out real-time monitoring of this molecule due to its harmful effects on human health. In this study, a highly sensitive SnO2/rGO gas-sensing material has been prepared by a hydrothermal method. The surface adsorption and reaction processes between the SnO2/rGO gas-sensing film and diethyl ether have been studied by the in situ diffuse-reflectance Fourier-transform infrared spectroscopy at different temperatures. The results show that the SnO2/rGO gas-sensing material has high sensitivity to diethyl ether, and the lowest detection limit can reach 1 ppm, and that ethyl $\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}\mathop {{\rm{C}}{{\rm{H}}_{\rm{2}}}}\nolimits^ \cdot } \right)$, oxethyl $\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{C}}{{\rm{H}}_2}{{\rm{O}}^ \cdot }} \right)$, ethanol (CH3CH2OH), formaldehyde (HCHO), acetaldehyde (CH3CHO), ethylene (C2H4), H2O, and CO2 surface species are formed during diethyl ether adsorption at different temperatures. A possible mechanism of the reaction process is discussed.