The Gibbs free energy of MoS₂ for H⁺ absorption is near-zero, which is considered to be a promising cocatalyst for H₂ production. Nevertheless, the activity of MoS₂ for HER is greatly limited by the acidic environment. Herein, we study that Co-doped MoS₂ (Co-MoS₂) nanosheets can realize an extremely efficient photocatalytic H₂ production of g-C₃N₄ nanosheet (NSs) in alkalescent environment, such as triethanolamine (TEOA). The optimized Co-MoS₂/g-C₃N₄ hybrids exhibits extremely boosted photocatalytic H₂ evolution rate of 3193 μmol^-1h⁻¹ g⁻¹, approximately 2.4, 6.0 and 42.0 times as much as MoS₂/g-C₃N₄ (1326 μmol^-1h⁻¹ g⁻¹), CoS₂/g-C₃N₄ (530 μmol^-1h⁻¹ g⁻¹) and pure g-C₃N₄ (76 μmol^-1h⁻¹ g⁻¹), respectively. Besides, we calculated the apparent quantum efficiency (AQE) of all photocatalysts under the light at λ = 370 nm, and the AQE of Co-MoS₂/g-C₃N₄ hybrids reaches 16.62%. DFT calculation and experimental data reveal that the outstanding HER activity of Co-MoS₂/g-C₃N₄ hybrids is ascribed to the Co doping inducing the distortion of MoS₂ crystal, which effectively reduces the H binding free energy for HER. The project of Co-MoS₂/g-C₃N₄ hybrids provides experience on the progress of low-cost and highly effective photocatalysts for photocatalytic H₂ evolution.