Abstract: The application of hydrogen production technology through water electrolysis can promote the consumption of renewable energy and enhance the flexibility of power system regulation, especially in systems with a high proportion of renewable energy. Alkaline water electrolyzers（AWEs） are widely used in the field of industrial electrolysis due to their low cost, simple structure, and mature technology. However, the low electrolysis efficiency of AWES under low load conditions makes it difficult to effectively utilize the fluctuating renewable energy power over the wide range. To address this issue, this paper firstly reveals the mechanism behind the difference in high-and low-load efficiency from the perspective of the distribution of the exciting electric field inside the electrolytic cells. An optimal power pulse-width modulation（OP-PWM） strategy is proposed to reshape the internal electric field distribution under low load conditions. A two-stage converter for pulse electrolysis has been designed. And key control parameters are analyzed. Moreover, the proposed theory is validated through an experimental platform for photovoltaic direct-drive electrolytic hydrogen production. The experimental results show that the OP-PWM strategy can significantly improve the low-load efficiency compared to the dc electrolysis mode, with an increase of 1.8 times. Under the constraint of achieving an efficiency greater than 48%, the system operation has been improved from 28%-100% to 20%-100% of rated.