International commercial usages which differ from international commercial practice have the nature of source of law. International commercial usages have the basic characters of repeatedly practice，widely observed and opinion juri.The forms of international commercial usages include written and unwrit ten usages.As for the level effect of law，international commercial usages are lower than international treaties acceded or concluded by China and the laws of China. Subject to the principal of non-violation of the China'spublic interests，where the parties agreed or the matters not covered by the laws of China or intemational treaties acceded or concluded by China，then the international commercial usages shall be applied.