A method for searching across instant message systems and an interconnecting server are disclosed. The method includes the steps of searching in a SIMPLE IM system by a WV-IMPS user, and searching in a WV-IMPS system by a SIMPLE IM user. The interconnecting server includes a message input/output module and a message processing and converting module. The technical solution of the present invention seamlessly connects the search services of the WV-IMPS instant message system and the SIMPLE instant message system, and thus solves the problem on interconnecting search functions between different types of instant message systems.