The dynamics of decaying substances of plant residues during various decay periods was studied by using the DTA, TG and DTG analytic techniques. The results showed that the exothermic peaks at 330℃ in DTA curve was the specific peak of organic matter pyrolysis, and the dynamic energy characteristics of decaying substances of plant residues during decay process expressed by the enthalpy change (ΔH) of this exothermic peak were that the decay process of plant residues was a exothermic process as a whole, but it appeartd as an alternation process of endotherm and exotherm at some decay stage. Accorcding to the energy change charac-teristics the whole decaying process of plant rtsidues could be divided in to three stages, i.e., the fluotuating stage-the drastical decline stage-the stage tending to be stable. A significanx correlatiau was found between the enthalpy change (ΔH) and O.M.(%).Adding nitrogen could accelerate the decay process of plant residues and increase the energy flutuation extent at the fluctuating stage and shorten the drastical decline stage as well as result in advance of the stage tending to be stable. Whole decay process could be finished in eleven mouths under the experimental conditions. TG and DTG curves had the same characteristics as DTA.