A multi-rotor system (MRS) is defined as containing more than one rotor in a single structure. The shrouded wind turbine with a brimmed diffuser (B-DAWT) has demonstrated power augmentation for a given turbine diameter and wind speed by a factor of about 2-5 compared with a bare wind turbine. In the present research, B-DAWTs are used in a multi-rotor system. The power output performance of MRSs using two, three and five B-DAWTs in a variety configurations have been investigated, focusing on the aerodynamics of a MRS with multiple B-DAWTs, spaced in close vicinity in the same vertical plane. Power output increases of up to 8, 12 and 21% in average for a two, three and five-rotor MRS configuration are achieved in comparison to those for the stand-alone configuration. Thus, when B-DAWTs are employed as the unit of a MRS, the total power output is remarkably increased. As the number of units for a MRS is increased from two to five, the increase in power output become larger and larger. This is because that the gap flows between B-DAWTs in a MRS are accelerated and cause lowered pressure regions due to vortex interaction behind the brimmed diffusers. Thus, a MRS with more B-DAWTs can draw more wind into turbines showing higher power output.