The oxidation heat of coal is the direct reason leading to coal spontaneous combustion.When coal is exposed in oxygen atmosphere, the physical adsorption and chemisorption happened, and then which resulting chemical reaction followed heat between coal and oxygen. Owing to the complexity and uncertain of molecular structure of coal, it was only reduced that bridge bonds, side chains and O2-containing functional groups in coal may be prone to oxidation in last year, but not to deeply investigate into the structures and the type of the active radicals. In this paper, according to the last achievements in coal structure research, the hypomethylether bond,hypoalkyl bond of α-carbon atom with hydroxyl and α-carbon atom with hypomethy side chain and hypomettyl bonds linking up two aromatic hydrocarbon in bridge bonds, and methoxy, aldehyde and alkyls of α-carbon atom with hydroxy in side bonds are inferred to be free radical easily to lead to oxidize coal under the ambient temperature and pressure. The order from strong to week of oxide activation of the seven surface active groups is aldehyde side chains, hypomethylether bonds, hypoalkyl bonds of α-carbon atom with hydroxyl, hypoalkyl bonds of α-carbon atom with hypomethyl, hypomethyl bonds linking up two aromatic hydrocarbon, methoxy, alkyls side chains of α-carbon atom with hydroxyl. Because of the two unsaturated molecular tracks of C2, unpaired eleotron clouds of the part of surface active groups of coal enter molecular tracks of O2 to lead to chemisorb on the conjugate effect and induced effect of surface active groups, and then chemical reaction followed heat happens in them. On the basis of change of bond energy, weighted average method is adopted to count the reactionheat value of each mol CO, CO2 and H2O. The property of coal spontaneous combustion is different for the different number and oxidability of the active structure in the coal resulting in the different oxidation heat.