An advanced neutronics code system SARCS-4.0,which can simulate the core composed by arbitrary square assemblies,calculate Uranium-Plutonium and Thorium-Uranium cycle,treat many burnable poisons(such as B,Gd,Er,Hf,Ag,In,Eu,Sm.etc) and several control rod materials,is introduced in this paper.The SCWR reactor core is calculated by SARCS-4.0.The results show that SARCS-4.0 is accurate enough to design the reactor core.