The present disclosure provides a software upgrade system, which is applicable to at least one autonomous mobile robot installed with software in a data distribution service domain. The at least one autonomous mobile robot publishes a version information about the software to the version synchronization topic and receives other version information from the version synchronization topic. Also, the at least one autonomous mobile robot subscribes to a version synchronization topic, and takes the software of the at least one autonomous mobile robot itself as the latest version by a software update procedure to upload to a software update topic, or downloads the latest version of the software from the software update topic and installs it. The present disclosure provides a software upgrade method and a non-transitory recording medium.