On the basis of a literature analysis a new mathematical model of the ammonia oxidation process has been derived and implemented in an original numerical algorithm based on the finite element method. The model is capable of monitoring of reaction components concentrations, gas and gauzes temperatures throughout the catalyst bed as well as determination of influence of gauzes number on the ammonia oxidation efficiency. The model has been verified on the basis of experimental data obtained from a plant specially designed for investigation of this process. The comparison of the simulation results with the experiment proved a good description of the phenomena taking place during the catalyst ammonia oxidation process.