A control device, an air conditioner, and a control method thereof are provided. The control device includes a communication interface configured to communicate with an external device, and a processor configured to control the communication interface to receive indoor and outdoor environment information and user control information, and the processor is configured to predict an indoor temperature over time through a temperature prediction model based on the received indoor and outdoor environment information and the user control information, obtain a corresponding candidate setting temperatures, obtain temperature control schedules, predict energy consumptions of the obtained temperature control schedules, respectively, through a trained energy prediction model, identify a temperature control schedule with the smallest predicted energy consumption as an optimal temperature control schedule, and transmit control information over time to an air conditioner during a pre-set power saving operation time based on the identified optimal temperature control schedule.