A server and a controlling method of a server are provided. The server includes a communication interface, a memory configured to store priorities of each of a plurality of spaces, and a processor configured to control a plurality of air conditioners arranged in the plurality of spaces, and the processor may, based on a total power usage of the plurality of air conditioners exceeding a first threshold value, control the plurality of air conditioners to operate in a power peak control mode to reduce the total power usage, and based on the total power usage being less than a second threshold value while operating in the power peak control mode, control the plurality of air conditioners to sequentially switch to a general mode according to the priority.