In order to discover mechanism of the low-temperature oxidation（LTO）reaction of the heavy oil and their effect on the oil composition and property，taken Liaohe oilfield block Qi40 heavy oil as experimental sample，the low temperature oxidation mechanism and the effect of temperature and catalyst on LTO was studied in laboratory high temperature and high pressure reactor. The results showed that the system pressure decreased，oxygen content decreased and carbon hydrocarbon increased after LTO reaction. The oxygen consumption were 43.87%，58.46%，52.53% and 62.89%，respectively，after LTO reaction under 120℃， LTO reaction under 180℃，LTO reaction under 120℃ with catalyst and LTO reaction under 180℃ with catalyst，respectively.During LTO process，both bond breaking reaction of macromolecule and condensation reaction of micromolecule occurred in crude oil，which resulted in the crude oil contents of saturated hydrocarbon，aromatic hydrocarbon and asphaltene increased，while the gum decrease. The viscosity of crude oil was increased by 17.63%，34.00%，18.22% and 38.50%，respectively，after LTO reaction under 120℃，LTO reaction under 180℃，LTO reaction under 120℃ with catalyst and LTO reaction under 180℃ with catalyst， respectively. which was relative to the increase of the content of asphaltene. The LTO reaction rate and oxygen consumption was affected by reaction temperature and catalyst. The higher the reaction temperature，the faster the reaction，and the higher the oxygen consumption. Moreover，the addition of cobalt naphthenate and manganese naphthenate catalyst could enhance the LTO reactivity and increase reaction rate and oxygen consumption.