With the increasing demand of energy, technical research of how to enhance oil recovery of steam flooding for heavy oil reservoirs has attracted widespread attention at present. Air-injection is an effective technology that has been used to improve the development effect of steam flooding in heavy oil reservoirs. The low-temperature oxidation (LTO) reaction and the high-temperature combustion reaction are the main mechanisms of air-injection technology. The high-temperature combustion reaction can decompose the heavy component in heavy oil, but it requires a higher-temperature condition, which the steam flooding process cannot offer. In addition, the LTO reaction between air and heavy oil consumes the O-2, so the safety risk of explosion caused by the mixture of O-2 and hydrocarbon gas can be eliminated. Nevertheless, oil viscosity will increase. During the steam flooding process, an aquathermolysis reaction occurs between heavy oil and high-temperature water, which decreases the content of the heavy component in heavy oil. Besides, catalyst MnO2 promotes the reaction by decreasing the activation energy of the reaction. In this paper, several static oxidative decomposition experiments are conducted to study the change characteristics of pressure, gas composition, oil composition, and oil viscosity after the reactions with different temperatures, pressures, and water saturations. In addition, four dynamic displacement experiments are conducted to compare the displacement effect of different displacement methods, including N-2-injection displacement, air-injection displacement, steam flooding, and air-injection-assisted steam flooding. Experimental results show that air-injection can effectively improve the development effect of steam flooding in heavy oil reservoirs. Upgrading and viscosity reduction for heavy oil by the combination of the LTO reaction and the aquathermolysis reaction can slow down steam channeling and increase production rate, thereby enhancing the ultimate recovery of steam flooding.