The present disclosure provides a method and an apparatus for monitoring an abnormal host, and a data processing device. The method includes: host information of a deployed host is obtained from a controller, where the host information includes address information of the deployed host; routing information of a to-be-detected host is obtained, where the routing information includes the address information of the to-be-detected host; it is determined whether the address information of the deployed host includes the address information of the to-be-detected host; and it is determined that the to-be-detected host is an abnormal host when the address information of the deployed host does not include the address information of the to-be-detected host.