The present invention relates to a method for updating an image file that is performed by a server, when a workable image file pre-stored in a storage unit of said server needs to be updated by a new image file, that duplicates said workable image file to said storage unit as a backup image file, and then restarts said serve by invoking the operating system with said new image file, and if an operating system can not be successfully invoked with said new image file, said server automatically selects said backup image file to invoke the operating system and restore to the status before said update.