Visible-light-driven photocatalytic hydrogen evolution reaction (HER) is of far-reaching significance to address the energy and environmental issues. Owing to the seriously limited charge separation and surface catalytic conversion efficiency, cocatalyts especially noble-metals (e.g. Pt) are fundamentally required for this reaction. Transitional metal dichalcogenides (TMDs) represent a type of promising nonprecious cocatalysts, but they still lack effective strategies to optimize the performance. In this work, we report a rational design of MoSe2 to form interlayer-expanded 1T-phase structure, to maximize the cocatalytic activity for photocatalytic HER by optimizing the surface activation ability for reaction molecule at both edge and basal sites. In a practical photo catalytic reaction, when intergrated with a semiconductor (two-dimensional carbon nitride, 2D-C3N4), the hybrid exhibits a satisfactory hydrogen evolution rate (1672.6 mu mol g(-1) h(-1), with external quantum efficiency of 5.2% at 420 nm) that greatly higher than the normal spacing 2H-MoSe2 (186.7 mu mol g h(-1)) and most noble metals (e.g. Au, Ag, Pd). The giant improved HER performance strongly demonstrates the superiority of the presented phase and interlayer engineering strategy. The formation mechanism of the specialized structure and the key factor affecting the performance are also discussed. This work may provide new avenues for the design of TMDs-based catalysts toward HER application.