Iconicity as one of the hotly\|discussed issues at present in the linguistic and semiotic field.This paper attempts to define the term as “Linguistic symbols are iconically correspondent to their referent in sound,form and syntactic structure.” Then it explains the definiton in detail with English and Chinese examples.The paper introduces with emphasis the syntactic iconicity of distance,length,order and markedness,which are of great significance to the language research and teaching.The Theory of Iconicity is a great challenge to “Saussurean Theory of Arbtrariness” popular for one century,and also a forceful complement as well.