Alkaline water electrolyzers (AWEs) are widely utilized in the field of industrial electrolysis due to their low cost, simple structure, and mature technology. However, the low-load inefficiency of AWEs hinders the ability to effectively follow the fluctuating renewable energy in full range. Focusing on this issue, this paper reveals the electrolysis mechanism from the perspective of the distribution of the electric field. Moreover, an optimal power pulse-width modulation (OP-PWM) strategy is proposed to reconstruct the electric field under the low load state. Experimental results show that the OP-PWM strategy can greatly improve low-load electrolysis efficiency compared to the conventional DC power electrolysis mode.