Abstract: Gas-cooled fast reactor (GFR) is one of generation Ⅳ candidate reactor systems, featured with versatile usage because of high temperature, and economy because of fuel breeding. For a reference GFR core design, the criticality and burnup characteristics for the single assembly model and full core model were calculated through the coupling of MCNP and ORIGEN, and the differences in the calculation precision and calculation time were compared between the fine structure model and homogenized assembly model, respectively. As a result, the necessity and feasibility to adopt the homogenized assembly method in the GFR whole core burnup calculation were explained and discussed.