The disclosure relates to petrochemistry, gas chemistry, coal chemistry, particularly to a synthesis of hydrocarbons C5 and higher from CO and H2 under the Fischer-Tropsch reaction; the invention relates to a process and a system for producing synthetic liquid hydrocarbons. A process for producing synthetic liquid hydrocarbons is provided by catalytic converting syngas under the Fischer-Tropsch reaction on a fixed catalyst bed in a vertical shell and tube reactor with coolant supply into shell wherein as soon as the syngas conversion degree achieves 60-80%, a pressure gradient along the tubes is reduced below 0.1 bar/m and this value is maintained during the whole process. A reactor for Fischer-Tropsch synthesis is provided comprising tubes with catalyst in a shell, the ratio of the tube diameter at the tube outlet to the diameter at the inlet is from 1.5/1 to 2.5/1. The invention gives a possibility to achieve the optimum temperature range in the catalyst bed; it improves heat and mass-transfer and shut out an accumulation of the liquid products in the bottom of the tubes.