Molybdenum-based cocatalyst being used to construct heterojunctions for efficient photocatalytic Hsub.2 production is a promising research hotspot. In this work, CdInsub.2Ssub.4 was successfully closely supported on bulk Mosub.2C via the hydrothermal method. Based on their matching band structures, they formed a Type Ⅰ heterojunction after the combination of Mosub.2C (1.1 eV, −0.27 V, 0.83 V) and CdInsub.2Ssub.4 (2.3 eV, −0.74 V, 1.56 V). A series of characterizations proved that the heterojunction composite had higher charge separation efficiency compared to a single compound. Meanwhile, Mosub.2C in heterojunction could act as an active site for hydrogen production. The photocatalytic Hsub.2 production activity of the heterojunction composites was significantly improved, and the maximum activity was up to 1178.32 μmmol hsup.−1 gsup.−1 for 5Mosub.2C/CdInsub.2Ssub.4 composites. 5Mosub.2C/CdInsub.2Ssub.4 heterojunction composites possess excellent durability in three cycles (loss of 6%). Additionally, the mechanism of increased activity for composites was also investigated. This study provides a guide to designing noble-metal-free photocatalyst for highly efficient photocatalytic Hsub.2 evolution.