An embedded network device includes a memory, a NOR flash, a first part and a second part of old firmware. The NOR flash includes a first image sector which stores the first part of the old firmware, a second image sector which stores the second part of the old firmware, and a third image sector for backup the old firmware. The embedded network device obtains a first part and a second part of new firmware and store the new firmware in the memory, reads the first part of the old firmware from the first image sector and writes to the third image sector, reads the first part of the new firmware form the memory and writes to the first image sector, reads the second part of the new firmware from the memory and writes to the third image sector.