The exploration of highly active bifunctional electrocatalysts for acidic electrochemical water splitting has attracted wide attention due to their importance in polymer electrolyte membrane (PEM) electrolyzers. However, existing catalysts normally suffer from low catalytic efficiency under acidic conditions. Herein, we developed a series of Ir-doped CoP nanowires arrays on carbon cloth (Ir-CoP/CC) materials, realizing prominently improved bifunctional catalytic activity for overall water splitting in an acidic medium. The optimized Ir-4-CoP/CC catalyst exhibits the smallest overpotential of 38 mV and 237 mV to reach 10 mA cm(-2) for HER and OER, respectively. Through systematic experimental research, we find the best intrinsic activity belongs to Ir-3-CoP/CC catalyst, which presents superior bifunctional performance with the most economical usage of Ir. As a result, the best acidic water splitting electrolyzer displays a very low voltage of 1.50 V at 10 mA cm(-2). This work provides a novel strategy to develop highly active bifunctional catalysts for acidic electrochemical water splitting.