A grid-connected PV system has been proposed based on MMC (modular multilevel converter) under partial shading, followed by a design of the control strategy of the system. Each photovoltaic array is connected with a VSC by a DC-DC converter circuit, thus forming a sub-module PSM, PSM and reactor in series to form MMC. The whole control system includes the start-stop control, the maximum power point control, and the grid connected control system. The start-stop control adopts DC voltage control strategy in the energy feedback phase, three phase simultaneous discharge strategy is used in capacitor discharge phase. By using Matlab/Simulink simulation software, a simulation test of the system has been carried out, with its results to verify the effectiveness and feasibility of the system in that it helps to improve the solar energy utilization, reduce the harmonic content of the grid connected output waveform, and realize the independent control of the output power.