To achieve sustainable and clean energy for the hydrogen economy, developing efficient earth-abundant and non-noble transition metal photo/electrocatalysts toward overall water splitting is highly desirable. In this work, layered double hydroxide (LDH)@g-C3N4 composites with hierarchical flower-like micro/nanosheets and a high surface area have been synthesized by a solvothermal method. HRTEM images exhibit that the surface of the g-C3N4 nanosheets is highly orientated with the main exposure of the (002) plane. Compared with pristine CoFe-LDH, the hierarchical nanocomposite presents an excellent and stable elecrocatalytic performance in 1.0 M KOH, with a small Tafel slope of 58 mV dec-1 and an overpotential of about 275 mV at a current density of 10 mA cm-2. Simultaneously, CoFe-LDH@g-C3N4 exhibits an exceptional performance for the HER in 1.0 M KOH electrolyte, with an overpotential of 417 mV at a current density of 10 mA cm-2 and a small Tafel slope of 77 mV dec-1. Therefore, this work not only accomplishes improved catalytic activity of CoFe-LDH by the introduction of g-C3N4 nanosheets, but also provides an insight into the correlation between hierarchical flower-like morphologies and photo/electrochemical catalytic activity for overall water splitting