Abstract: 1999 Montreal convention is an important result of modernization and consolidation of Warsaw liability system by air transportation and is put into force by 2003. It symbolizes that the law of international air transportation liability has get into a new stage. With the method of analysis, this essay will explore the relationship between Montreal convention and Warsaw liability system and conclude its new developments. At last, it puts forward that some important points of legislation have been transferred from protecting carrier interests to consumer interests, and objectivity and being unlimited are common treads for international private aviation law of the 21st century.