Forest fire often causes death of a large quantity of trees. There was a great difference in decay degree among dead woods in the burned area. In order to analyze the differences in pyrolysis between rotten wood and normally growing wood, a thermogravimetric experiment was conducted using victimized rotten wood and the wood of normally growing tree of 12 main tree species in “3·29” forest fire burned area in 2006 in Anning, Kunming. The activation energy, ignition temperature, burnout temperature and comprehensive indexes of 24 samples were analyzed and calculated. The research showed that the thermal stability of rotten wood was greater than that of the wood of the normally growing tree. The burning rate of normal tree wood was higher than that of the rotten one.