Structure and phase engineering in low-cost and earth-abundant MoS2 materials have been widely explored in catalytic domains. Designing MoS2 nanostructures associated with the number of catalytically active edge sites is of particular importance for obtaining an effective HER photocatalytic system. We herein report hydrothermal-synthesized defect-rich O-incorporated 1T-MoS2 nanosheets (denoted as DRM), and their implementation as cocatalysts to form photocatalytic heterostructure with CdS nanorods (denoted as DRM-C). For comparison, defect-free O-incorporated 1T-MoS2 nanosheets (denoted as DFM) and corresponding heterostructure i.e. DFM-C were simultaneously synthesized. A carefully comparative study on DRM and DFM demonstrates that the DRM cocatalyst exhibits more abundant defects in the basal planes and edges, and thus leading to the higher density of active sites beneficial to the photocatalytic HER. As a result, the optimized 20 wt% DRM-C exhibits an extraordinary visible-light (lambda > 420 nm) photocatalytic H-2 production rate of 132.4 mmol h(-1) g(-1), obviously higher than that of 20 wt% DFM-C (102.1 mmol h(-1) g(-1)). Interestingly, such an impressive activity of 20 wt% DRM-C is demonstrated to be superior to that of pure CdS (20.0 mmol h(-1) g(-1)) and conventional Pt/CdS (89.0 mmol h(-1) g(-1)). To the best of our knowledge, this DRM-C photocatalyst shows the advanced visible-light driven HER performance among reported MoS2/CdS composites.