A chiller system and a control method thereof includes a plurality of chiller modules in which a refrigeration cycle is performed to supply cold water, a main control device generating an operation signal to simultaneously or successively operate the plurality of chiller modules, a module control device provided in each of the plurality of chiller modules to control an operation of each of the plurality of chiller modules on the basis of the operation signal of the main control device, and a starting device communicably connected to the module control device to selectively apply power into the plurality of chiller modules.