Herein, cobalt–graphene–silica nanocomposites were prepared by a sol–gel method to produce heavy hydrocarbons for Fischer–Tropsch synthesis. The catalysts were characterized by N₂ physisorption, XRD, TEM, TPR, TPD, XPS, and DRIFTS techniques. The activity of catalysts and the selectivity of products were examined in a tubular fixed-bed reactor. It can be concluded that the introduction of graphene into cobalt–silica nanocomposites significantly enhanced the amount and stability of adsorbed CO at low temperatures, resulting in higher concentrations of CO species on the catalyst surface. Moreover, graphene can weaken the cobalt–silica interaction, leading to higher degree of reduction of cobalt oxides and higher adsorption amounts of H₂. In addition, the introduction of graphene led to the formation of cobalt with smaller particle sizes, which contributed to great enhancement of CO conversion. The selectivity to methane distinctly decreased to 4.2% from 8.1%, whereas the selectivity to C₅⁺ products increased from 84.5% to 92.4%. The α value increased from 0.89 for the Co–Si catalyst to 0.94 for the Co–0.1GSi catalyst. In addition, with the increase in the graphene content, the fraction of heavy hydrocarbons (C_19–29) for catalysts evidently increased to 36.0% from 28.3%, but the fraction of naphtha (C_5–12) clearly reduced to 17.7% from 27.7%.