Straight run diesel catalytic hydroisomerization mathematical model has been developed. There are the following steps for sequential accomplishment: assessment of thermodynamic possibility of spontaneous reactions under the existing technological conditions, development and formalization of hydrocarbon reaction network scheme, kinetic parameters evaluation, industrial verification of the model. The temperature impact within 345405 °C, the pressure impact in the range of 5-8 MPa and hydrogen bearing gas consumption impact within 3000-51000 m3/h on higher molecular n-alkanes conversion and i-alkanes yield as the basic components which determine diesel fuels low-temperature characteristics to the fullest extent, have been investigated using the developed model. It has been revealed that hydroisomerization process ought to be carried out under such temperature and pressure which do not lead to catalyst exploitation properties come-down in order to receive the product with the required low temperature characteristics. They are 355 °C and 6,7 MPa. The optimal hydrogen bearing gas consumption has been adopted as 39000 m3/h when the feed flow rate is 301 m3/h.