The main aspects of mathematical modeling of diesel fuel are considered. It is shown that all industrial types of reactor units are essentially equivalent to a single large reactor. It is proposed to characterize the feedstock as a mixture or a combination of several narrow fractions, wherein the aggregate of organosulfur impurities in each of these narrow fractions is considered as one pseudo-component in which the total sulfur content is equal to the sulfur content in the narrow fraction. The possibility of minimizing the loading of the catalyst into the reaction unit during separate hydrogenation of raw materials previously fractionated into light and heavy broad fractions was proved. The necessity of replacing the concept of reaction rate constant with the kinetic characteristic of hydrotreating as a multicomponent chemical process is substantiated. The kinetic characteristic can be approximated by a simple hyperbolic equation. Mathematical modeling of hydrotreating of real diesel fuel indicates the acceptability of the proposed new calculation methods.