Abstract: The objective of the work presented in this paper consists of evaluating, by a numerical method, the distribution of electromagnetic energy in the centre of a cavity. More precisely it is the observation of the electromagnetic field around a device under test. The numerical technique which we opted is Transmission Line Matrix (TLM) which is based on time domain. The possible targeted applications are, on one side, the analysis of a measurement techniques e.g. Mode Stirrer Reverberating Chamber (MSRC) and on the other side the analysis of electromagnetic environment of a system.