In order to carefully analyze the accuracy of the relativistic MRSF-TDDFT (SOC-MRSF), the SOC-corrected energy levels of C, Si, Ge and Sn atoms were considered, since both accurate high-level calculations and experimental data of those atoms are available. Following these atomic systems, SOC-MRSF was applied to the real molecular systems of 4-thiothymine, which has a third-row element of Sulfur. Finally, the chance of the intersystem crossing (ISC) in thymine was investigated.