The purpose of the study is to determine the physical essence of numeric values of a layout factor of the particulate matter filter in the exhaust system of the diesel plant for the mathematical mod el of its operational efficiency. Physical essence of this factor is that it makes it possible to take into account the influence of temperature of exhaust gases of the diesel engine at the inlet to the housing of the filter, which affects the course of processes of condensation of products of incomplete combustion of fuel on particulate matters and coagulation of particulate matters themselves in the flow of exhaust gases and, as a consequence, dimensions of particulate matters. The temperature of exhaust gases in such statement varies depending on location of the filter along the exhaust tract of the diesel engine (due to processes of extension of exhaust gases flow and heat exchange with the environment), as well as by the modes of external velocity characteristic of the diesel engine. Such influence was explored experimentally at the engine test bench with the autotractor diesel engine 2Ch10.5/12. The methods of obtaining the source data for the construction of the coefficient were described. Ecological parameters of exhaust gases of the diesel engine for different locations of the filter, received by direct and indirect measurements, were approximated by the linear regression method and formed the basis for the definition of numeric values and the formula to determine layout factor of the exhaust system. We established and mathematically described quantitative and qualitative relationships between indicators of operational efficiency of the particulate matter filter and the temperature of exhaust gases of the diesel engine 2 Ч 10.5/12 at the inlet to the filter.