The present invention relates to a functional coating agent having antimicrobial activity and water-repellency/oil-repellency at the same time, a method for preparing the same, and a coating method using the same. Specifically, the present invention relates to a method for preparing a coating agent which provides antimicrobial activity to a water-repellent/oil-repellent nanocoating in order for smart devices, etc., such as touch-type displays, to be used hygienically, and a coating method using vacuum deposition equipment.