A study on oxidation characteristics of heavy oil is the basis of mine design of improving oil recovery by in-situ combustion. However，there are relatively few studies on the effect of pressure on high-pressure in-situ combustion of heavy oil reservoirs. In order to clarify the influence of pressure on oxidation characteristics of heavy oil reservoirs by insitu combustion and effectively reduce the adverse effects of high-pressure in-situ combustion，this paper took Lukeqin heavy oil reservoirs as an example and investigated the thermal weight loss，heat release，and other oxidation characteristics of heavy oil reservoirs under different pressures based on thermogravimetric and differential scanning calorimetry experiments. The paper first calculated the kinetic parameters under different pressures and obtained the activation energy and reaction enthalpy at each oxidation stage. Secondly，the combustion effect and stability of in-situ combustion under varied pressures were evaluated through the combustion tube experiments. The experimental results show that higher pressures accelerate the oxidation reaction rates of heavy oil and intensify heat release. The oxidation paths of complex systems are changed，and the characterization parameters of reaction kinetics need to be modified under high pressures.In addition，the advancing speeds of the in-situ combustion line under high pressures are accelerated，and the temperatures of the burning fronts are more than 300 °C higher than those of atmospheric-pressure in-situ combustion；the combustion stability becomes worse，and the combustion under high-pressure in-situ combustion with oxygen reduced by 10% is stable，which effectively suppresses the combustion instability caused by fast high-pressure reaction speeds.