Developing high-efficient and low-cost photocatalysts is of great significance yet challenging for photo-catalytic hydrogen evolution. Herein, we report a 2D/2D Ru-modulated CoP nanosheets (Ru-CoP-x, where x refers the Ru-to-Co molar ratio)/g-C3N4 nanosheets (GCN NSs) ternary hybrid as a photocatalyst for hydrogen evolution under visible light. The optimal photocatalyst 25% Ru-CoP-1:8/GCN NSs exhibits an excellent hydrogen evolution rate of 1172.5 mmol g(-1) h(-1) under visible light with a high apparent quantum efficiency (AQE) of 3.49% at 420 nm, which is close to Pt/g-C3N4 photocatalytic system and higher than most reported transition metal phosphides (TMP)/g-C3N4 photocatalytic system. Experimental results indicate that the higher photocatalytic hydrogen evolution performance can be mainly attributed to the binary Ru-CoP-x co-catalyst with efficient charge separation and promoted surface water reduction kinetics, and the 2D/2D self-assembly structure with strong interface Schottky effect and short charge transport distance. This study provides a new approach to develop cost-effective Pt-alternative co-catalysts for photocatalytic hydrogen evolution by incorporating a small amount of ruthenium into the transition metal phosphides. (C) 2020 Elsevier Inc. All rights reserved.