An unprecedented photocatalyst, Smsub.2EuSbOsub.7, was successfully fabricated in this paper, through a high-temperature solid-state calcination method, which represented its first ever synthesis. Additionally, using the solvothermal method, the Smsub.2EuSbOsub.7/ZnBiSbOsub.5 heterojunction photocatalyst (SZHP) was fabricated, marking its debut in this study. XRD analysis confirmed that both Smsub.2EuSbOsub.7 and ZnBiSbOsub.5 exhibited pyrochlore-type crystal structures with a cubic lattice, belonging to the Fd3m space group. The crystal cell parameter was determined to be 10.5682 Å or 10.2943 Å for Smsub.2EuSbOsub.7 or ZnBiSbOsub.5, respectively. The band gap width measured for Smsub.2EuSbOsub.7 or ZnBiSbOsub.5 was 2.73 eV or 2.61 eV, respectively. Under visible light irradiation for 150 min (VLTI-150 min), SZHP exhibited remarkable photocatalytic activity, achieving 100% removal of parathion methyl (PM) concentration and 99.45% removal of total organic carbon (TOC) concentration. The kinetic constant (k) for PM degradation and visible light illumination treatment was determined to be 0.0206 minsup.−1, with a similar constant k of 0.0202 minsup.−1 observed for TOC degradation. Remarkably, SZHP exhibited superior PM removal rates compared with Smsub.2EuSbOsub.7, ZnBiSbOsub.5, or N-doped TiOsub.2 photocatalyst, accompanied by removal rates 1.09 times, 1.20 times, or 2.38 times higher, respectively. Furthermore, the study investigated the oxidizing capability of free radicals through the use of trapping agents. The results showed that hydroxyl radicals had the strongest oxidative capability, followed by superoxide anions and holes. These findings provide a solid scientific foundation for future research and development of efficient heterojunction compound catalysts.