An application executing method for automatically executing an application stored in a storage unit of an external storage device in an operating system (OS) of a computer host is provided. The method includes dividing the storage unit into a first partition and a second partition; emulating the first partition as compact disc-read only memory (CR-ROM); storing a switch program in the first partition; and storing the application in the second partition. The method also includes providing only the first partition to be accessed by the OS and automatically executing the switch program by the OS to decouple and re-couple the external storage device to the computer host. Additionally, the method further includes providing only the second partition to be accessed by the OS and executing the application when the external storage device is re-coupled to the computer host.