The dual-core fiber is a special optical fiber,which has the special refractivity distribution,and the devices based on dual-core fiber are applied in many fields.The development of dual-core fiber is introduced briefly,then the types of dual-core fiber and its basic characteristics are described.Moreover,the principle of coupling filters and interferometers based on dual-core fiber and their improved technology are introduced emphatically,and other applications are introduced.Finally a conclusion is given.