The development of an efficient, fast, and real-time sensor for detecting dibutylamine (C8H19N) gas remains challenging. In this study, a simple controllable and environmentally friendly solvothermal method was used to construct novel Fe2O3/MgFe2O4 nanotube array structures with heterointerfaces. The array structure exhibits a relatively large specific surface area and high-activity heterointerfaces. These features greatly promote the diffusion and adsorption of gas molecules onto the sensitive layer, effectively increasing the surface-adsorbed oxygen species and active sites of the sensing material. The sensing performance of the Fe2O3/MgFe2O4 array structure for C8H19N gas is greatly improved due to the synergistic effect of these multiple factors. The sensor showed a high response of 92.6 to 100 ppm C8H19N at 170 °C, with a short response time of 3.6 s and an ultra-low detection limit of 10 ppb. The sensitization mechanism of Fe2O3/MgFe2O4 to C8H19N was investigated by combining theoretical calculations and experimental techniques. This study broadens the application of gas sensors for the detection of volatile organic compounds (VOCs).