A method is for updating an original firmware file of an I/O module which communicates with multiple host-end devices and stores the original firmware file. The method includes: receiving a current-received data packet from one host-end device; when it is determined that the current-received data packet is a first data packet constituting an update file, and that the original firmware file is not undergoing an update process, setting a status flag to indicate that the original firmware file is undergoing an update process, storing the current-received data packet; and repeating the previous steps when it is determined that the current-received data packet is not a last one data packet constituting the update file.