Herein, an efficient CoS_x/twinned-Cd_0.5Zn_0.5S (CoS_x/T-CZS) photocatalyst was successfully constructed by an in situ deposition method. Notably, the establishment of the zinc-blende/wurtzite (ZB/WZ) homojunction in T-CZS and the heterojunction between CoS_x and T-CZS can facilitate the charge separation in the bulk and surface of T-CZS, simultaneously. As a consequence, T-CZS exhibited much higher activity compared to the zinc blende Cd_0.5Zn_0.5S (ZB-CZS) and wurtzite Cd_0.5Zn_0.5S (WZ-CZS) with single-phase. After introducing amorphous CoS_x, the H₂ evolution rate of 4 wt% CoS_x/T-CZS reached 76.2 mmol h⁻¹ g⁻¹ in 20 vol% triethanolamine (TEOA) aqueous solution under 300 W Xe lamp irradiation at 30 °C, which was nearly 5.9 times higher than that of pure T-CZS. The excellent activity is mainly attributed to the avoidance of rapid recombination of bulk and surface photogenerated electron–hole pairs through the synergistic effect of the homo-heterojunction structure. In addition, the good optical absorption abilities of CoS_x/T-CZS and their photo-electrochemical properties are helpful to improve the reactivity of CoS_x/T-CZS. This work provides new ideas for constructing noble metal-free photocatalysts with homo-heterojunction.