Since traditional mechanical switches cannot meet the needs of today’s distribution network, flexible multi-state switches based on cascaded H-bridge converters have great advantages as a new type of power electronic device to replace traditional mechanical switches. However, based on the novel shared module flexible multi-state switching topology, the traditional control method is no longer applicable, so a new modulation method is urgently needed. Aiming at the above problems, this paper proposes a new square-wave-like modulation method. The square-wave-like modulation adds zero-level time to the square-wave-modulation to reduce the instantaneous voltage change value of the shared module at the zero-crossing point. At the same time, the phase of the modulated wave can be variable by coordinating the relationship between the zero-level time and the phase, thereby avoiding the occurrence of overmodulation of non-shared modules. Finally, the correctness and effectiveness of the new modulation strategy are verified by building a three-phase experimental platform.