Abstract: Numerical analysis is carried out for the effects of four kinds of grid spacer on the resistance characteristics within sub-channels of supercritical reactor core with commercial CFD code using unstructured polygonal mesh. The results show that the pressure loss induced by the grid spacer includes the frictional drag and form drag. The frictional drag is mainly determined by the length of grid strap while the form drag is determined by the blockage ratio of grid spacer and the structure of flow enhancing feature. Due to the more streamlined structure, the mixing-van type grid spacer induces less pressure loss when it is used to enhance forced convection within sub-channel. Although the mixing-van type grid spacer has more complex structure in comparison with standard egg-crate grid spacer, it has obvious advantages in the area of flow enhancing and can be primarily considered in the optimal design of grid spacer used in supercritical water cooled reactor core.