The thermal analyses (DTA and TG) of various organo-mineral complexes is seven soil types of Tibet were carried out based on the fractionation and assessment of soil organic matter. The results show that the degree of organo-mineral completation in the test soils was lower. The loosely combined carbon and tightly combined carbon occupied a relatively dominant position in total completed carbon. Exothermic peaks were found at about 310℃ and 430℃ for original soil samples and its various organo-mineral completes. Another etothermic peak at 510℃ existed in a few soil samples in the study. An obvious，weight loss followed each etothermic peak. From the results of the thermal analyses (DTA and TG) and the fractionation and assessment of organic matter in the soils discussed, it can be concluded that the heavy fraction of organic matter stably and tightly combined with soil mineral particles was the dominant factor of the etothermic peak at 310℃, the loosely combined organic matter was pyrolyzed at about 430℃, and the light fraction of organic matter which did not complex with soil minerals was pyrolyzed at about 510℃. The results also indicated that the pyrolytic enthalpy changes (ΔH) of organic matter in the alpine steppe soil and subalpine steppe soil were greater than those in the alpine meadoav soil and subalpine meadow soil respectively.