In recent years, there have been many studies on photocatalytic water splitting, but there are still few high-efficiency photocatalysts for photocatalytic seawater splitting. In this study, a series of hollow Co sulphide-supported CdS catalyst (H–CoS/CdS) composite photocatalysts were prepared by loading CdS onto the surface of H–CoS, which can be used for efficient H 2 production in pure water and simulated seawater. The heterojunction H–CoS/CdS exhibited H 2 production of 572.4 μmol g −1 (4 h) from simulated seawater, which is 97.7 and 2.96 times those of H–CoS and CdS, respectively. The h-CoS cocatalyst extended the light absorption range of CdS, improved the chemical stability, and significantly enhances the charge separation efficiency. This study provides guidance for the reasonable design of a photocatalytic seawater-based H 2 production catalyst with high efficiency and low cost. • A hollow CoS/CdS heterojunction photocatalyst was prepared by the template method. • The H–CoS/CdS-2 photocatalyst exhibited exceptional activity for H 2 production. • H 2 production reached 572.4 μmol g −1 after 4 h in simulated seawater.