Abstract: The reaction products of n-hexane and n-dodecane linear alkanes in nitric acid system were determined by infrared spectroscopy, gas chromatography-mass spectrum and nuclear magnetic carbon spectrum. The effects of temperature, nitric acid concentration and reaction time on the n-hexane and n-dodecane nitration products were quantitatively analyzed by gas chromatography. The pressure change of n-hexane and n-dodecane with nitric acid at a temperature of 150 ℃ using a high pressure reactor was investigated. The results show that the reaction products of n-hexane and n-dodecane in the nitric acid system at high temperature are a mixture of nitrohexane isomers(2-nitrohexane and 3-nitrohexane) and a mixture of nitrododecane isomers(2-, 3-, 4-, 5-, 6-nitrododecane). The temperature and nitric acid concentration are the greater factor impacting on degradation products, while the reaction time affects smaller. When the temperature is 150 ℃, the maximum pressure of n-hexane in the nitric acid system is 3.44 MPa, which is much higher than the pressure of 1.58 MPa of the n-dodecane system. And as the proportion of nitric acid increases, the pressure and the degree of reaction generated by the reaction system increase.