The present disclosure provides a cable modem and an operating method thereof. This method includes steps as follows. After receiving a boot command, it is checked whether a boot data of a main storage area of a flash memory is complete. When the boot data of the main storage area of the flash memory is not complete, a backup data is copied from a backup storage area to overwrite the boot data of the main storage area. Then, the boot data in the main storage area is used to continue the boot process.