As a new type of power electronic device to replace traditional mechanical switches,the soft open point (SOP) has the advantages of fast response speed and controllable power flow. In this paper,a novel cascaded H-bridge SOP with shared modules is proposed,which simplifies its structure and saves some modules. However,the traditional control method is no longer applicable,so a new square-wave-like modulation method suitable for common modules is proposed in this paper. Firstly,the modulation wave of the shared module is calculated according to the specific working conditions,and then the modulation wave of the non shared module is calculated in coordination to achieve the modulation of all modules of the new topology. Square-wave-like modulation adds zero level time on the basis of square wave modulation to reduce the instantaneous change value of shared module voltage during zero crossing. At the same time,the phase of the modulated wave can be changed by coordinating the zero level time and phase relationship to avoid the occurrence of over modulation of non shared modules. Finally,a three-phase experimental platform with common module SOP is built to verify the correctness and effectiveness of square-wave-like modulation strategy.