Photocatalysts with novel structure and superior hydrogen (H₂) evolution activity are attractive to solve energy shortage and other environmental problems. As one of two-dimensional transition metal disulfides (2D TMDs), MoS₂ cocatalyst with a unique lamellar flower-like porous structure was fabricated herein to boost the photocatalytic H₂ evolution of CdS. The porous MoS₂/CdS photocatalyst reached a H₂ evolution activity of 54.1 mmol h⁻¹ g⁻¹, which is 36 times better than in case of pure CdS. Characterizations demonstrated that the promoted activity of the porous MoS₂/CdS composite was strongly related to the distinctive cocatalyst structure. The coexistence of spherical porous and lamellar structures, as well as a heterojunction structure between MoS₂ and CdS played crucial roles. A slow photo effect helped to enhance the visible-light utilization. The heterojunction structure of CdS particles with lamellar MoS₂ accelerated the transfer of photo-induced electrons. This unique porous 2D TMD structure as a cocatalyst is expected to enhance activities for H₂ evolution of other photocatalysts as well.