Photocatalysts play an important role in solving energy problems, and Z-scheme heterojunctions have garnered significant interest due to their ability to efficiently separate photogenerated carriers and improve redox capacity. In this work, we construct a Z-scheme heterojunction by substituting Se and Te for S atoms in the SWSiN2 bilayer. The findings demonstrate that they have high kinetic stability, and the construction of heterojunctions can narrow the bandgap, effectively improving light absorption. The existence of the built-in electric field can be explained by studying the charge density difference, which breaks through the band gap limitation in water photocatalytic splitting. Their photocatalytic characteristics with and without strain are described in depth, with the spectroscopic limited maximum efficiency (SLME) of TeWSiN2/SWSiN2 surpassing 30 % under no strain. With tensile strain, SeWSiN2/SWSiN2 energy bands rise, but TeWSiN2/SWSiN2 energy bands decrease. Meanwhile, the band edge arrangement of XWSiN2/SWSiN2 (X=Se; Te) becomes smaller with increasing strain. The spectral finite maximum efficiency of SeWSiN2/SWSiN2 increases from 12 % to 27 % and shows good light absorption (ηSTH = 10.60 % for SeWSiN2/SWSiN2, ηSTH = 14.17 % for TeWSiN2/SWSiN2) and carrier utilization.