This work concerns the modelling of the plasma of a pulsed microwave discharge in nitrogen. The goal is to determine the temporal variations of the densities of the respective plasma species. The ultimate goal is to adopt the methods developed for these calculations for discharges in polluted air or flue gas. A global numerical model is formulated. The object modeled is the plasma of a microwave torch operating at atmospheric pressure. The set of equations for the model consists of particle balance and power balance equations. The most important reactions between the plasma species are only taken into account. The rate coefficients for processes involving electrons are calculated based on a solution of the Boltzmann equation for the electrons. Diffusion and heat transfer are modelled with the aid of terms reflecting also the discharge geometry.