Today, organic phosphorus compounds (OPC) are actively exploring all the main scientific centers of the world, as determined by their chemical benefits, the importance of the activity of organisms and great potential practical use in industry, fire safety, agriculture and everyday life. There are some different points of view on the reaction mechanisms of inhibiting action of OPC on the combustion, that can be presented as number of different reactions with active centers of flame H•, O••, OH• participation. In the experimental work  showed that the OPC has extinguishing properties, but the mechanism at the elementary reactions not yet finally clarified. In the work of Werner and Cool , a reaction path of OPC destruction to form a molecule of CH3PO2. In , this channel is secondary. On the contrary, it is argued that the destruction occurs mainly through methylphosphonate and further to phosphoric acid. A model for the study is the following. First of all we have calculated energy gap corresponding chemical bonds in the molecule of researched extinguishing agent then gradually have calculated the interaction energy of each of the products formed from the degradation with the active centers of the flame. For the development of mechanisms of the inhibitory effects of OPC on the flame possible ways of thermal degradation of this compound quantum chemical ab initio (6-31 G*) method have been examined. The research has showed that the thermal degradation of OPC molecules occurs by gradual elimination of atoms and groups of atoms. It is Werner-Cool  point of view on the OPC destruction mechanism. So, theoretical calculations helped us to predict the most probably reaction ways in the complicated chemical processes.