Systems of differential rate equations characteristic for several basic types of plasma chemical reactions have been obtained. Every system permits one to reproduce a full kinetic picture of the reaction (kinetic curves of the starting, intermediate, and final compounds) and identify its mechanism by comparing this picture with the experimental kinetic pattern. The four important cases of a gas-phase plasma polymerization were considered in detail : radical propagating chain and stepwise recombination-activation, each having two different mechanisms of the death of plasma radicals. A comparison between the theoretical and experimental (mass spectrometry) kinetic patterns of six starting monomers and their low-molecular-weight products has established the chain mechanism predominating in all cases at the initial stages of the synthesis.