Herein we report a heterostructure with ultrathin nanosheets of Co-doped molybdenum sulfide on CdS nanorod array (donated as CdS@CoMo2S4/MoS2) by hydrothermal synthesis. Firstly, elemental Co doping MoS2 (CoMo2S4) delivers the double benefits of increased active sites and enhanced conductivity. Secondly, the structural characteristics maximally exposes the MoS2 edges and enlarges interfacial contact area between the composite catalyst and electrolyte, as well as the efficient interfacial charge transfer. The ratio of CoMo2S4/MoS2 in CdS@CoMo2S4/MoS2 plays a crucial role for the enhanced photo-assistant electrocatalytic hydrogen evolution reaction (HER). We can tune the ratio of CoMo2S4/MoS2 by controlling the preparation time or the ratio of precursor of Co/Mo. The catalyst with predominant MoS2 phase shows superior photocatalytic HER performance with a high H-2 production rate of 46.60 mu mol mg(-1) h(-1). Meanwhile, the catalyst with predominant CoMo2S4 phase exhibits not only relatively low overpotential of 172 mV at 10 mA cm(-2), which outperforms most values that have been reported on catalyst supported on ITO substrate, but also possesses H-2 production rate of 23.47 mu mol mg(-1) h(-1). The superior photo-assistant electrocatalytic HER activity results from the synergistically structural and electronic modulations, as well as the proper energy band alignment between MoS2 and CdS. This investigation could provide an approach to integrate the electro- and photo catalytic activities for HER, especially the photo responding behaviour at a bias potential which is meaningful to produce H-2 for actual application. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.