Abstract: In order to reduce the number of control rods, the burnable poison (BP) is used to control excess reactivity in supercritical water cooled reactor (SCWR). Overall BP designs, the design in which rare-earth oxide mixes with fuel is widely used in SCWR. After comparing four kinds of rare-earth oxide, Er₂O₃ is chosen as BP. The effect of different BP loading patterns on assembly performance was analyzed. The safety of annular fuel assembly was estimated with different BP containments. Core performances with and without BP were compared. The results show that the core radial power peaking factor decreases by introducing BP. It is also shown that the core axial power peaking factor increases and the power peak moves towards the top of the core. The reason of this effect was studied. Two optimizations, decreasing the temperature of lower plenum and increasing the gradients of axial enrichments, were given based on this study. By applying these optimizations, the core axial power peaking factor and maximum cladding surface temperature decrease.